T he use of flux response analysis in the determination of kinetic parameters for heterogeneous catalysts is demonstrated. Reaction rates and conversions for the decomposition of ammonia over a Pt/alumina catalyst are measured. Both steady-state and pulse-type experiments are described. For the first time, the conversions calculated using flux response analysis are independently checked by measuring the composition of the exit gas using a mass spectrometer and found to be in excellent agreement. This is only possible for steady-state experiments. For the pulses the flux response method is found to be much more successful at measuring the conversion than the available mass spectrometry facilities. The order of reaction with respect to ammonia is estimated at 0.7, which is consistent with other published data for catalytic ammonia decomposition.