New Jersey v. Portash

In New Jersey v. Portash (440 U.S. 450 [1979]), the Supreme Court held that the threatened use of defendant's immunized Grand Jury testimony for impeachment purposes should the defendant take the stand was such an error, requiring reversal without resort to a harmless error analysis even though the defendant did not take the stand. The Court equated use of such immunized testimony to the use of coerced confessions which are inadmissible for all purposes.