The kinetics of the consecutive H-D exchange reactions between methane and deuterated acid FAU- and MFI-type zeolites was studied with on-line mass spectrometric product analysis, in the temperature range 450 to 550 degrees C. On both zeolite types, the rate constant of H-D exchange increases with decreasing Al content. At the same Al content, the reaction rate constant of MFI is ca. three times larger than that of FAU, showing that chemical composition and structural effects are important in determining the rate of exchange. The apparent activation energy is in the range 122-150 kJ/mol, independent of the Al content and structure type. A kinetic isotope effect of approximately 1.7 was found, which is in disagreement with the earlier proposed concerted reaction mechanism (G. J. Kramer, R. A. van Santen, C. A. Emeis, and A. K. Nowak, Nature 363, 529, 1993). (C) 1999 Academic Press.