dissenting.
In my view the Court’s holding that mandamus lies in this case cannot be squared with the course of decisions to which the majority at the threshold pays lip service. Ante, pp. 109-110. As the Court recognizes, mandamus, like the other extraordinary writs, is available to correct only those decisions of inferior courts which involve a “usurpation of judicial power” or, what is tantamount *128thereto, “a clear abuse of discretion”; such a writ “is not to be used as a substitute for appeal.” Ibid.
Mandamus is found to be an appropriate remedy in this instance, however, because (1) petitioner’s challenge was based on an asserted lack of power in the District Court to issue the examination order, and (2) that being so, the Court of Appeals had the right also to inquire into the application of the “in controversy” and “good cause” requirements of Rule 35 (a), particularly since those issues, like the ..question 'of “power,” were matters of “first impression” which in “these special circumstances” 'should be determined by the Coúrt of Appeals “so as to avoid piecemeal litigation and to settle new and important problems.” Ante, p. 111.
For me - this reasoning is unacceptable. Of course a court of appeals, when confronted with a substantial challenge to the power of a district court to act in the premises may proceed to examine that question without awaiting its embodiment in a final judgment, as the Court of, Appeals did here by issuing an order to show cause why a writ of mandamus should not issue. But once it is determined that the challenged power did exist, and that the district court acted within the limit of that power, an extraordinary writ should be denied. I know of no case which suggests that a court of appeals’ right to consider such a question at an interlocutory stage of the litigation also draws to the court the right to consider other questions — here the “in controversy” and “good cause” issues — which, otherwise would not be examinable upon a petition for an extraordinary writ. Indeed, were an extraordinary writ to issue following a determination that the district court , lacked power, that would put an end to the litigation and these questions would never be reached. A.nd, as the Court correctly states, the fact that “hardship may result from delay and perhaps unneces*129sary trial,” ante, p. 110, is not a factor that makes for the issuance of such a writ.
Manifestly, today’s procedural holding, when stripped of its sugar-coating, is born of the Court’s belief that the petitioner should not be exposed to the rigors of these examinations before the proper “guidelines” have been established by this tribunal. Understandable as that point , of view may be, it can only be indulged at the. expense of making a deep inroad into the firmly established federal policy which, with narrow exceptions,1 permits appellate review only of the final judgments of district courts. To be sure the Court is at pains to warn that what is done today puts an end to future “interlocutory” review of Rule 35 questions. Ante, p. 112. Nevertheless,. I find it hard to escape the conclusion that this decision may ópen the door to the extraordinary writs being used to test any question of “first impression,” if it can be geared to an alleged lack of “power” in the district court. As such, it seems to me out of keeping with the rule of “finality,” with respect to which Congress, wisely I think, has been willing to make only cautious exceptions.2'
The Court of Appeals having correctly concluded, as this Court now holds and as I agree, that the District Court had power to order the physical and mental examinations of this petitioner, and since I believe that there was no clear abuse of discretion in its so acting, I think the lower court was quite right in denying mandamus, and I would affirm its judgment on that basis.
See, e. g., 28 U. S. C. §§ 1292 (a)(1), (b) (1958 ed.).
See note 1, supra.