concurring in the result.
Because of the importance of this case to the administration of criminal justice in the federal courts, I believe it appropriate to set forth briefly the different route by which I reach the same result as does the Court.
Ford and Matusow, as the Court’s opinion indicates, were crucial government witnesses because their testimony supplied the principal evidence relating to the period immediately surrounding the filing of petitioner’s allegedly false affidavit. Cross-examination brought out *673the fact that each had made oral or written reports to the Federal Bureau of Investigation relating to the respective events about which each had testified on direct examination. Having established that fact, petitioner sought an order requiring the Government to produce, for inspection by the court, the reports relating to those matters about which each witness had testified. The procedure to be followed was carefully specified: the court was to determine whether the reports had evidentiary value for impeachment of the credibility of Ford or Matusow; if the court found that they had value for that purpose, it was then to make them available to petitioner for his use in cross-examination. The Government opposed each motion on the ground that no showing of contradiction between the witness’ testimony and his reports had been made as required by a controlling Fifth Circuit decision, Shelton v. United States, 205 F. 2d 806. Apparently on that ground, the trial court denied the motions.
Petitioner’s requests were limited to a narrow category of reports dealing with specified meetings and conversations. The purpose of the requests — to impeach the credibility of crucial government witnesses — was made clear. Petitioner did not ask to inspect the documents himself; he sought access only to those portions of the reports which the trial court might determine to have evidentiary value for impeachment purposes, and to be unprivileged.1
*674I agree that, under such circumstances, it was unnecessary for petitioner to show that Ford’s and Matusow’s trial testimony was contradicted in some respect by their contemporaneous reports. Although some federal courts have required a showing of contradiction,2 this Court never has done so.3 A rule requiring a showing of contradiction in every case would not serve the ends of justice. I concur, therefore, in that portion of the Court’s opinion holding that petitioner laid a sufficient foundation for the production of the reports.
1 would not, however, replace the inflexible and narrow rule adopted by the courts below with the broader, but equally rigid rule announced by the Court. In matters relating to the production of evidence or the scope of .cross-examination, a “large discretion must be allowed the trial judge.” Goldman v. United States, 316 U. S. 129, 132; Glasser v. United States, 315 U. S. 60, 83; Alford v. United States, 282 U. S. 687, 694. The appropriate determination of a motion to produce reports made in connection with the examination of a witness depends upon the significance of the facts sought to be established, *675and upon the potential use of the requested document in proving those facts. Since that determination depends on “numerous and subtle considerations difficult to detect or appraise from a cold record . . . ,” the trial court’s discretion should be upheld in the absence of a “clear showing of prejudicial abuse of discretion . . . .” Cf. Michelson v. United States, 335 U. S. 469, 480. We have so held even when the documents sought to be produced have been used at the trial for the purpose of refreshing a witness’ recollection. United States v. Socony-Vacuum Oil Co., 310 U. S. 150, 232-234. When the documents have not been so used and are sought only to impeach the credibility of adverse witnesses, and not to prove the facts stated therein, the same conclusion is even more compelling.
The Court goes beyond the request of petitioner that reports be produced for examination by the trial court and, in effect, seems to hold that the Government waives any privileges it may have with respect to documents in its possession by placing the author of those documents on the witness stand in a criminal prosecution. The Government’s privileges with respect to state secrets and the identity of confidential informants embody important considerations of public policy. They are peculiar privileges in that they require the withholding of evidence not only from the jury, but also from the defendant. See Roviaro v. United States, 353 U. S. 53 (identity of informers); Reynolds v. United States, 345 U. S. 1 (state secrets). Once the defendant learns the state secret or the identity of the informer, the underlying basis for the privilege disappears, and there usually remains little need to conceal the privileged evidence from the jury. Thus, when the Government is a party, the preservation of these privileges is dependent upon nondisclosure of the privileged evidence to the defendant. This makes it *676necessary for the trial court, before disclosing the privileged material to the defendant, to pass on the question by examining in camera the portions claimed to be privileged. Cf. Bowman Dairy Co. v. United States, 341 U. S. 214, 221. There is nothing novel or unfair about such a procedure. According to Wigmore, it is customary.
. . it is obviously not for the witness to withhold the documents upon his mere assertion tha.t they are not relevant or that they are privileged. The question of Relevancy is never one for the witness to concern himself with; nor is the applicability of a privilege to be left to his decision. It is his duty to bring what the Court requires; and the Court can then to its own satisfaction determine by inspection whether the documents produced are irrelevant or privileged. This does not deprive the witness of any rights of privacy, since the Court’s determination is made by its own inspection, without submitting the documents to the opponent’s view . . . (Emphasis deleted and supplied.) VIII Wigmore, Evidence (3d ed. 1940), 117-118.
Numerous federal decisions have followed this practice with respect to the type of documents here involved— contemporaneous reports made by a government investigator or informer who later testifies at the trial.4 This procedure protects the legitimate public interest in safeguarding executive files. It also respects the interests of justice by permitting an accused to receive all informa*677tion necessary to his defense. The accused is given an opportunity to argue that the privilege asserted by the Government is inapplicable and that, even if applicable, his need for the evidence, under the circumstances of the case, outweighs the Government’s interest in maintaining secrecy. The problem is closely related to that involved in Roviaro v. United States, supra, dealing with the necessity of the disclosure of an informer’s identity in a criminal case. There this Court said:
“[N]o fixed rule with respect to disclosure is justifiable. The problem is one that calls for balancing the public interest in protecting the flow of information against the individual’s right to prepare his defense. Whether a proper balance renders nondisclosure erroneous must depend on the particular circumstances of each case, taking into consideration the crime charged, the possible defenses, the possible significance of the informer’s testimony, and other relevant factors.” 353 U. S., at 62.
The trial judge exercises his discretion with knowledge of the issues involved in the case, the nature and importance of the Government’s interest in maintaining secrecy, and the defendant’s need for disclosure. By vesting this discretion in the trial judge, the conflicting interests are balanced, and a just decision is reached in the individual case without needless sacrifice of important public interests.5
*678I also disagree with the Court’s holding that the failure to produce the records to petitioner necessitates a new trial. Petitioner requested only that the records be produced to the trial court.6 He is entitled to no more. Whether a new trial is required should depend on the contents of the requested reports. If the reports contain material that the trial court finds has evidentiary value to petitioner, a new trial should be granted in order that petitioner may use it. But if the reports do not contain contradictory or exculpatory material helpful to petitioner, no possible prejudice could have resulted from the trial court’s denials of petitioner’s motions.7 Were it not for the fact that I believe the trial court committed reversible error in instructing the jury with respect to the meaning of membership and affiliation, I would vacate the judgment below and remand to the trial court with instructions to examine the reports and to determine, in the light of the entire record, whether the failure to produce the reports was prejudicial to petitioner.8
However, I believe the trial court failed to give the jury sufficient guidance with respect to the meaning of the phrases “member of the Communist Party,” and *679“affiliated with such party” as they are used in § 9 (h) of the Labor Management Relations Act, 61 Stat. 146, 29 U. S. C. § 159 (h). The instruction given as to membership was as follows:
“In considering whether or not the defendant was a member of the Communist Party, you may consider circumstantial evidence, as well as direct. You may consider whether or not he attended Communist Party meetings, whether or not he held an office in the Communist Party, whether or not he engaged in other conduct consistent only with membership in the Communist Party and all other evidence, either direct or circumstantial, which bears or may bear upon the question of whether or not he was a member of the Communist Party on April 28, 1950.”
This instruction failed to emphasize to the jury the essential element of membership in an organized group — the desire of an individual to belong to the organization and a recognition by the organization that it considers him as a member.9
The instruction on affiliation also was defective. After quoting dictionary definitions employing synonymous words, the trial court merely said: “Affiliation . . . means something less than membership but more than sympathy. Affiliation with the Communist Party may be proved by either circumstantial or direct evidence, or both.” This instruction allowed the jury to convict petitioner on the basis of acts of intermittent cooperation. It did not require a continuing course of conduct “on a fairly permanent basis” “that could not be abruptly ended without *680giving at least reasonable cause for the charge of a breach of good faith.” 10
Because of these errors in the instructions, petitioner is entitled to a new trial. Accordingly, I concur in the judgment of the Court.
In his brief, petitioner states:
“Petitioner asked only that the reports be produced to the trial judge so that he could examine them and determine whether they had evidentiary value for impeachment purposes. Petitioner sought access only to those portions of the reports having this value. The motion therefore proposed no broad foray into the government’s files and afforded the judge every opportunity to protect the government’s legitimate privilege as to the matters not connected with this case.”
Scanlon v. United States, 223 F. 2d 382, 385-386; Shelton v. United States, 205 F. 2d 806, 814-815; Christoffel v. United States, 91 U. S. App. D. C. 241, 244r-247, 200 F. 2d 734, 737-739, rev’d on other grounds, 345 U. S. 947; D’Aquino v. United States, 192 F. 2d 338, 375; United States v. De Normand, 149 F. 2d 622, 625-626; United States v. Ebeling, 146 F. 2d 254, 257; Little v. United States, 93 F. 2d 401; Arnstein v. United States, 54 App. D. C. 199, 203, 296 F. 946, 950.
In Gordon v. United States, 344 U. S. 414, the petitioners had shown that written statements given to government agents by a key government witness contradicted the witness' trial testimony. In holding that the trial court erred in denying petitioners’ motion for the production and inspection of these statements, the Court was deciding that case on its facts. I do not regard it as establishing a rule that a showing of contradiction is an essential element of the foundation precedent to production.
See, e. g., United States v. Coplon, 185 F. 2d 629, 638; United States v. Beekman, 155 F. 2d 580, 584; United States v. Cohen, 145 F. 2d 82, 92; United States v. Krulewitch, 145 F. 2d 76, 79; United States v. Flynn, 130 F. Supp. 412; United States v. Mesarosh, 116 F. Supp. 345, 350; United States v. Schneiderman, 106 F. Supp. 731, 735-738.
Privileged material sometimes can be excised from the reports without destroying their value to the defendant. Only when deletion is impracticable is the court compelled to choose between disclosing the document as a whole and withholding it completely. • Material withheld from the defendant should be sealed as part of the record so that an appellate court may review the action of the trial court and correct any abuse of discretion.
See n. 1, supra.
Rule 52 (a) of the Federal Rules of Criminal Procedure provides: “Any error, defect, irregularity or variance which does not affect substantial rights shall be disregarded.” See Lutwak v. United States, 344 U. S. 604, 619; Kotteakos v. United States, 328 U. S. 750, 756-777. There are many cases in which nonproduction of documents has been held to be harmless error. Three comparatively recent cases, dealing with reports of law-enforcement officers are United States v. Sansone, 231 F. 2d 887; Montgomery v. United States, 203 F. 2d 887, 893-894; and Bundy v. United States, 90 U. S. App. D. C. 12, 193 F. 2d 694.
The trial court is the appropriate forum to consider the possible prejudicial effect of the error. See, e. g., Communist Party v. Subversive Activities Control Board, 351 U. S. 115; Remmer v. United States, 347 U. S. 227.
Fisher v. United States, 231 F. 2d 99, 106-107. See also, Ocon v. Guercio, 237 F. 2d 177; Baghdasarian v. United States, 220 F. 2d 677; Sigurdson v. London, 215 F. 2d 791; Dichhoff v. Shaughnessy, 142 F. Supp. 535.
United States ex rel. Kettunen v. Reimer, 79 F. 2d 315, 317. See also, Bridges v. Wixon, 326 U. S. 135; Fisher v. United States, 231 F. 2d 99, 107-108.