Abstract: A study has been made of the interaction of azobenzene vapor with a series of cation-exchanged montmorillonites. Cu 2+ -and Ag+ -clays give basal spacings ⩾ 20Å. The azobenzene retains its trans conformation in the clay and can be extracted with ether. If the intercalate is heated above 120°C then there is catalytic decomposition leaving a black product. Infrared spectra of an extract from this product suggests that it might be made up of a mixture of amines. A photo-electron spectroscopic study shows that the nitrogen is in two distinct chemical environments both in the initial and in the blacked intercalates. The C:N ratio remains at 6:1 throughout.