A defense attorney called upon to give testimony before a grand jury investigating his client ceases to be an advocate for his client and becomes a potential witness against him. The client's sixth amendment right to a fair trial and adequate representation by counsel are threatened. Recent cases at the federal district and circuit courts of appeals are discussed, with special emphasis on In re Grand Jury Subpoena for Attorney Representing Criminal Defendant Jose Evaristo Reyes-Requena, a case in which the federal government is appealing a Texas district court judge's decision to quash a subpoena requiring an attorney to testify before a grand jury investigating his client. 15 footnotes.