The Government (P) believed that Kastigar et al. (Ds) were likely to assert their Fifth Amendment privilege. Prior to the scheduled appearances, P applied for an order directing Ds to answer questions and produce evidence before the grand jury under a grant of immunity conferred pursuant to 18 U.S.C. §§ 6002-6003. Ds were granted use immunity, but not from subsequent prosecution for the crime involved. Ds refused to testify on grounds that the use immunity statute did not adequately protect them from self-incrimination. The District Court rejected this contention and ordered Ds to appear before the grand jury and answer its questions under the grant of immunity. Ds appeared but refused to answer questions asserting their privilege against compulsory self-incrimination. The court found them in contempt and committed them to the custody until either they answered the grand jury's questions or the term of the grand jury expired. Ds appealed, and the court of appeals affirmed. The Supreme Court granted certiorari.