(concurring specially):
Although I agree with the result reached by Judge Coleman’s application of the evidentiary principle denominated “opening the door”,1 I do so for slightly *213different reasons. As expounded upon by Judge Coleman, this principle may be susceptible to treatment as an intractable rule, the violation of which is grounds for reversal per se. Since the Supreme Court has chosen to delimit the categories of trial court evidentiary errors which must invariably result in reversal,2 I would have misgivings about any decision which could be construed to expand that list.
Rather, I choose to bottom my opinion on the ground that what transpired in the proceedings below jeopardized Pa-quet’s right to a fair trial. In reaching this conclusion I am mindful of the words of Justice Harlan that:
[T]he Federal Constitution does not guarantee trial procedures that are the best of all worlds, or accord with the most enlightened ideas of students of the infant science of criminology, or even those that measure up to the individual predilections of members of this Court.3
Nevertheless, the presence of a confluence of factors impels me to the aforementioned conclusion.
The substance of the exchange about which Paquet sought to testify served as the exclusive basis for his entrapment defense. As Judge Coleman eloquently indicates, once the government introduced a portion of the conversation between Christian and Paquet through one of its agents, Paquet should have been permitted to fully explain the conversation from his point of view. The unfairness occasioned by the curtailment of his testimony was aggravated by the fact that after both the government and Paquet had completed their cases, the government was permitted to present Mr. Christian as a rebuttal witness. It appears to me that his testimony constituted much more than rebuttal. Although a self-confessed perjurer, Christian, if believed, served to bolster and substantially strengthen the government’s case. Indeed, he was permitted to place his “gloss” on the conversation after the court had refused to entertain Paquet’s. In these circumstances, a denial of the right of Paquet to explain the conversation and the subsequent appearance of Christian as a so-called rebuttal witness very likely gave the jury the impression that the government’s version of the conversation was the correct one.
It may be argued that in view of evidence seriously implicating Paquet in the commission of the crime with which he is charged and the opportunity he had in examining Christian to fully expose those aspects of their exchange which supported his entrapment defense, whatever error committed by the trial judge was harmless. In my view, whatever force this argument has derives *214largely from its generality, and is attenuated when applied to the instant case. Certainly, the fact that Paquet may have committed a crime cannot vitiate any impropriety attendant to the curtailment of his attempt to establish a defense. Courts are particularly reluctant to deem error harmless where, as here, the error precludes or impairs the presentation of an accused’s sole means of defense.4 Nor can the errors be considered harmless under the putative theory that by availing himself of the opportunity to elicit testimony from Christian concerning those aspects of the conversation most favorable to his defense, Paquet could have fully exposed his position to the jury. In my view, a surrogate explanation by Christian, a government witness, would be an inadequate substitute for Paquet’s own testimony, where Paquet’s own testimony was curtailed without explanation to the jury as to the reasons therefor while the government’s evidence on the same matter was permitted.5
It is not my purpose to suggest a per se rule for the orderly presentation of evidence or the sequence which should be followed in the prosecution of a criminal case. Indeed, this court has assiduously adhered to the rule that a trial judge must remain free to exercise his discretionary powers to promote the ends of justice.6 However, we have just as scrupulously applied the principle that it is the trial judge’s duty “to conduct an orderly trial and to make certain as far as possible, that there is no misunderstanding of the testimony.” 7 In view of the fact that the rulings of the district court were not clear and explicit, and that no explanation of the reasons for such rulings was proffered to the jury, the district court was remiss in complying with its duty. This noncomplianee, when coupled with the rejection of Paquet’s explanation of the conversation between Christian and himself, substantially prejudiced Paquet’s trial. For the above mentioned reasons I concur in the decision to reverse the judgment of conviction.
. The principle has been invoked by both the Supreme Court and this court in the remote past. See Carver v. United States, 164 U.S. 694, 697, 17 S.Ct. 228, 41 L.Ed. 602 (1897) ; Stevenson v. United States, 86 E. 106, 110-111 (5th Cir. 1898). Other circuits have recently given it expression in a variety of contexts. See, e. g., United States v. Miriam, 422 F.2d 150, 153 (6th Cir.), cert, denied, 399 U.S. 910, 90 S.Ct. 2199, 26 L.Ed. 2d 561 (1970) (oral statements made by defendant to IRS agent) ; United States v. *213Littwin, 338 F.2d 141, 145 (6th Cir. 1964), cert, denied, 380 U.S. 911, 85 S.Ct. 896, 13 L.Ed.2d 797 (1965) (tape recording) ; United States v. Bohle, 445 F.2d 54, 66 (7th Cir. 1971) (medical record) ; Harris v. Smith, 372 F.2d 806, 816-817 (8th Cir. 1967) (medical record). See also Durham v. Cox, 328 F.Supp. 1157, 1165 (W.D.Va. 1971) (confession).
. In Chapman v. California, 386 U.S. 18, 23 n. 8, 87 S.Ct. 824, 17 L.Ed.2d 705 (1967), the Supreme Court noted only 3 situations in which error of even constitutional dimension is harmful per se: first, admission into evidence of a coerced confession; second, denial of the right to counsel, and third, trial by an impartial judge. I do not understand the Supreme Court’s opinion in United States v. Carver, supra, to elevate the open-door principle to a constitutional right. Even if my understanding is incorrect, since the Court had Carver before it when it enunciated the error per se categories in Chapman, it is hazardous to maintain that the “open-door” principle is an additional category.
In United States v. Bohle, supra, 445 F.2d at 66, the Eighth Circuit Court of Appeals refused to hold that a trial court’s violation of the open-door principle was an absolute ground for reversal.
. McGautha v. California, 402 U.S. 183, 221, 91 S.Ct. 1454, 28 L.Ed.2d 711 (1971). Cf. Lutwak v. United States, 344 U.S. 604, 619-620, 73 S.Ct. 481, 97 L.Ed. 593, rehearing denied, 345 U.S. 919, 73 S.Ct. 726, 97 L.Ed. 1352 (1953) ; Bruton v. United States, 391 U.S. 123, 135, 88 S.Ct. 1620, 20 L.Ed.2d 476 (1968) ; Smith v. Smith, 454 F.2d 572, 578-579 (5th Cir. 1971).
. See, e. g., Braswell v. Wainwright, 463 F. 2d 1148 (5th Cir. 1972) (exclusion of defendant’s sole witness who, without knowledge of defendant, had violated sequestration order held denial of due process) ; United States v. Minor, 459 F.2d 103 (5th Cir. 1972) (exclusion of record of state court adjudication of incompetency not harmless in criminal prosecution wherein defendant raised insanity defense, despite fact that defense witnesses had testified as to defendant’s adjudication of incompetency). See also Eli Lilly & Co., Inc. v. Generic Drug Sales, Inc., 460 F.2d 1096, 1105 (5th Cir. 1972) (reversible error to curtail discovery of sole grounds of defense in civil case).
Where the excluded evidence is merely corroborative, this court is more likely to find its exclusion harmless. See, e. g., United States v. Miles, 445 F.2d 974, 976-977 (5th Cir.), cert, denied, 404 U.S. 912, 92 S.Ct. 231, 30 L.Ed.2d 185 (1971).
. A broader rationale, but one not tantamount to a per se rule, is that secondary evidence is an inadequate substitute for primary evidence concerning the critical grounds for defense. Cf. United States v. Minor, supra.
. United States v. Jacquillon, 469 F.2d 380, 387 (5th Cir. 1972). Cf. Bursten v. United States, 395 F.2d 976, 982 (5th Cir. 1968).
. Posey v. United States, 416 F.2d 545, 555 (5th Cir. 1969), cert, denied, 397 U.S. 946, 90 S.Ct. 964, 25 L.Ed.2d 127, petition for rehearing denied, 397 U.S. 1031, 90 S.Ct. 1267, 25 L.Ed.2d 544 (1970). See United States v. Owens, 453 F.2d 355, 356 (5th Cir. 1971) ; O’Brien v. United States, 411 F.2d 522, 523 (5th Cir. 1969) ; Kyle v. United States, 402 F.2d 443, 444 (5th Cir. 1968).