H-D exchange between perdeuterioisobutane and NaH-Y-zeolites and H-mordenite (H-M) was studied using the pulse technique. Nine of the ten D atoms in the isobutane molecule were exchanged for H on the most acidic Y-zeolites at the lowest temperature (200 degrees C) where H-D exchange was observed, while other transformations of isobutane were not. The reaction is thought to be initiated by protonation of the tertiary C-D bond on the Bronsted acid sites of the catalyst and the exchange to proceed via the t-butyl carbenium ion intermediate. Release of the ion from the surface occurs via hydride transfer conserving the identity of the tertiary position. At higher temperatures and over the more acidic H-mordenite at even lower temperature (125 degrees C) an extensive intermolecular H-D exchange occurs between perdeuterioisobutane and its exchanged products. A more detailed understanding of this reaction chemistry is developed herein.