Per Curiam.
Petitioner, who is confined in a California state prison, sought to file a petition in forma pauperis for a writ of injunction in the District Court below. That court denied leave to proceed in forma pauperis, holding that petitioner was not entitled to the benefits of 28 U. S. C. § 1915 because he was no longer a “citizen” as required by that section. The District Court reached that decision in reliance on California Penal Code § 2600, which provides that one sentenced to imprisonment for a term of years is deprived of his civil rights for the period of imprisonment. The decision of the District Court is in error. Citizenship for the purpose of in forma pauperis proceedings in the federal courts is solely a matter of federal law. Congress has not specified criminal convictions, except for desertion and treason, as grounds for loss of citizenship. 8 U. S. C. § 801.
Petitioner thereafter filed a motion in the Court of Appeals for the Ninth Circuit for allowance of an appeal from the order of the District Court. The denial by a District Judge of a motion to proceed in forma pauperis is an appealable order. 28 U. S. C. § 1291; see Cohen v. Beneficial Industrial Loan Corp., 337 U. S. 541 (1949). The Court of Appeals, however, held that it had “no power to grant an application for allowance of an appeal,” and dismissed the petition.
Finally, petitioner filed in this Court a motion for leave to file a petition for a writ of mandamus to the District Court. Mandamus is an extraordinary remedy, available only in rare cases. Ex parte Collett, 337 U. S. 55, 72 (1949), and cases there cited. Because of the ambiguous state of this record, and the fact that a denial of this motion will not prejudice petitioner in further attempts to proceed in forma pauperis, the motion must be denied.
It is so ordered.
Mr. Justice Frankfurter took no part in the consideration or decision of this case.