delivered the opinion of the Court.
This is a direct appeal from the District Court for Northern Illinois prosecuted pursuant to the Criminal Appeals Act.1 It presents a question upon which the lower federal courts have sharply divided.2 The question is whether one who, in obedience to a subpoena, appears before a grand jury inquiring into an alleged violation of the Sherman Act, and gives testimony under oath substantially touching the alleged offense, obtains immunity from prosecution for that offense, pursuant to the terms of the Sherman Act, although he does not claim his privilege against self-incrimination.
The Sherman Act3 provides in part:
. . no person shall be prosecuted or be subjected to any penalty or forfeiture for or on account of any transaction, matter, or thing concerning which he may testify or produce evidence, documentary or otherwise, in any proceeding, suit, or prosecution under said Acts [the Interstate Commerce Act, the Sherman Antitrust Act, and other acts]; Provided further, that no person so testifying *426shall be exempt from prosecution or punishment for perjury committed in so testifying.”
That statute was supplemented by the Act of June 30, 1906,4 which, so far as material, is
“. . . under the immunity provisions [of the above Act and others] immunity shall extend only to a natural person who, in obedience to a subpoena, gives testimony under oath or produces evidence, documentary or otherwise, under oath.”
An indictment was returned charging corporations and individuals, including the two appellees, with conspiracy to fix prices in violation of the Sherman Act. The appellees filed special pleas in bar, each alleging that, in obedience to a subpoena duly served, he appeared as a witness for the United States before the grand jury inquiring respecting the matters charged in the indictment, and gave testimony substantially connected with the transactions covered by the indictment. No question is made but that the testimony so given did substantially relate to the transactions which were the subject of the indictment.
The United States demurred to the pleas as insufficient, since neither alleged that the witness asserted any claim of privilege against self-incrimination and therefore neither the Fifth Amendment of the Constitution nor the immunity statute could avail him.
The District Court overruled the demurrers on the ground that the plain mandate of the statute precluded prosecution of the appellees whether they had claimed the privilege or not. We hold that the decision was right.
Beyond dispute the appellees were entitled to immunity from prosecution if the statute is to be given effect as it is written. We are asked, however, to read into it a qualification to the effect that immunity is not obtained unless the privilege against self-incrimination is claimed. Inas*427much as the statute is addressed to this privilege, and the privilege is accorded by the Fifth Amendment, it is said that if immunity is offered as a substitute for the privilege, the immunity, like the privilege, ought to be claimed; that thus the statute and the Fifth Amendment, which are pari materia, will be given a consistent construction.
In the second place, it is urged that qualification of the forthright terms of the statute is necessary in order to avoid an unreasonable, unfair, and unintended result. The argument runs that if the statute is construed automatically to grant immunity without a claim of privilege, the prosecutor is at a disadvantage, since he does not know whether, or to what extent, a witness may have participated in a crime; and so runs the risk of unintentionally affording immunity. On the other hand, so it is said, the witness has full knowledge as to the nature of his own conduct, and as to his possible incrimination by testimony, and it is not unfair to require him to claim his privilege and so put the prosecutor on notice that, if he insists upon the testimony, the witness will obtain immunity.
The well-understood course of legislation before and after the adoption of the statute involved, and the legislative history, compel rejection of the contentions.
The Fifth Amendment declares that “No person . . . shall be compelled in any criminal case to be a witness against himself.” An investigation by a grand jury is a criminal case.5 The Amendment speaks of compulsion. It does not preclude a witness from testifying voluntarily in matters which may incriminate him. If, therefore, he desires the protection of the privilege, he must claim it or he will not be considered to have been “compelled” within the meaning of the Amendment.6
More than seventy years ago Congress was advised that, in suits prosecuted by the United States, where *428evidence had been sought from certain persons, to be used by the Government, they had interposed a claim of privilege which had been sustained by the courts.7 In order to forestall the obstruction and delay incident to judicial determination of the validity of the witness’ claim, and in order to obtain necessary evidence, even though the claim were well founded, Congress adopted the Act of February 25,1868,8 which became R. S. 860. This Act applied to all judicial proceedings and provided, in effect, that no evidence obtained from a witness could be used against him in a criminal proceeding.
This court, in Counselman v. Hitchcock, 142 U. S. 547, held the Act unconstitutional because, while it prevented the use of the evidence against the witness, it did not preclude his prosecution as a result of information gained from his testimony. The court indicated clearly that nothing short of absolute immunity would justify compelling the witness to testify if he claimed his privilege.
The original Interstate Commerce Act9 contained an immunity provision in the form held invalid in the Counselman case. To meet the decision in that case, Congress passed the Act of February 11, 1893,10 which applied only to proceedings under the Interstate Commerce Act. This statute, however, became the model for immunity provisions which were enacted at various times up to 1933, including the Act of February 25, 1903, supra, with which we are here concerned. This court sustained the constitutionality of these Acts.11
In 1906 the District Court for the Northern District of Illinois held, in United States v. Armour & Co., 142 F. 808, that a voluntary appearance, and the furnishing of *429testimony and information without subpoena, operated to confer immunity from prosecution under the Sherman Act. The court held that the immunity conferred was broader than the privilege given by the Fifth Amendment. The decision attracted public interest since, if it stood, one could immunize himself from prosecution by volunteering information to investigatory bodies. Congress promptly adopted the Act of June 30, 1906, supra, providing that the immunity should only extend to a natural person who, in obedience to a subpoena, testified or produced evidence under oath. The Congressional Record shows that the sole purpose of the bill was exactly what its language states.12 Senator Knox, who sponsored the bill, stated: “Mr. President, the purpose of this bill is clear, and its range is not very broad. It is not intended to cover all disputed provisions as to the rights of witnesses under any circumstances, except those enumerated in the bill itself.”
It is evident that Congress, by the earlier legislation, had opened the door to a practice whereby the Government might be trapped into conferring unintended immunity by witnesses volunteering to testify. The amendment was thought, as the Congressional Record demonstrates, to be sufficient to protect the Government’s interests by preventing immunity unless the prosecuting officer, or other Government official concerned, should compel the witness’ attendance by subpoena and have him sworn.
Not until 1933 did Congress evidence an intent that if the witness desired immunity he must, in addition, assert his constitutional privilege. In a series of acts adopted between 1934 and 1940 an additional provision was inserted adding this requirement.13 These acts indicate *430how simple it would have been to add a similar provision applicable to the Interstate Commerce Act, the Sherman Act, and others which have been allowed to stand as originally enacted save for the amending Act of 1906.14
The legislation involved in the instant case is plain in its terms and, on its face, means to the layman that if he is subpoenaed, and sworn, and testifies, he is to have immunity. Instead of being, a trap for the Government, as was the original Act, the statutes in question, if interpreted as the Government now desires, may well be a trap for the witness. Congress evidently intended to afford Government officials the choice of subpoenaing a witness and putting him under oath, with the knowledge that he would have complete immunity from prosecution respecting any matter substantially connected with the transactions in respect of which he testified, or retaining the right to prosecute by foregoing the opportunity to examine him. That Congress did not intend, or by the statutes in issue provide, that, in addition, the witness must claim his privilege, seems clear. It is not for us to add to the legislation what Congress pretermitted.
We have referred to the diversity of views amongst the lower courts. The Government insists that this court has settled the question in favor of its view. Its reliance is upon Heike v. United States, 227 U. S. 131. That case, however, decided only that the immunity conferred by the legislation in question was intended to protect the witness to the same extent that the Fifth Amendment protects him. The question was whether the immunity extended to prosecution for crimes with which the matters testified to were but remotely connected. This court held that, as the Amendment did not justify a claim of *431privilege against such remote contingencies, the immunity should be likewise construed not to reach them. The question of the necessity of a witness before an investigatory body claiming his privilege in order to earn his immunity was not decided.
The judgment is
Affirmed.
Act of March 2, 1907, 34 Stat. 1246, as amended by the Act of May 9, 1942, 56 Stat. 271, 18 U. S. C. 682.
Compare United States v. Armour & Co., 142 F. 808; United States v. Skinner, 218 F. 870; United States v. Elton, 222 F. 428; United States v. Lee, 290 F. 517; Johnson v. United States, 5 F. 2d 471; United States v. Lay Fish Co., 13 F. 2d 136; United States v. Greater New York Live Poultry C. of C., 33 F. 2d 1005, with United States v. Pardue, 294 F. 543; United States v. Ward, 295 F. 576; United States v. Moore, 15 F. 2d 593; United States v. Goldman, 28 F. 2d 424.
Act of February 25, 1903, c. 755, 32 Stat. 854, 904, 15 U. S. C. 32.
34 Stat. 798,15 U.S.C.33.
Counselman v. Hitchcock, 142 U. S. 547, 562.
United States ex rel. Vajtauer v. Commissioner, 273 U. S. 103, 113.
Cong. Globe, 40th Cong., 2d Sess., pp. 950-51, 1334.
15 Stat. 37.
24 Stat. 383.
27 Stat. 443, 49 U. S. C. 46.
Brown v. Walker, 161 U. S. 591.
40 Cong. Rec. 5500, 7657-58; 8734-39-40.
See e. g. Securities Exchange Act, 48 Stat. 900, 15 U. S. C. 78u (d); Investment Advisers Act, 54 Stat. 853, 15 U. S. C. 80b-9 (d).-
It may be, that, due to the thoroughness of preliminary investigation in the classes of cases in question, Congress has believed that the Government’s representatives needed no further warning of the result of subpoenaing a witness and examining him under oath.