Design of a chemically inert, ultrahigh-vacuum-compatible, pulsed gas inlet system is described. The inlet design is suitable for any gases compatible with glass, Teflon, and perfluoroalkoxy materials. The performance is illustrated by results for hydrazine decomposition on a planar model Ir/Al2O3/NiAl(110) catalyst. The inert, pulsed inlet system makes it possible to measure decomposition products evolving from a small (2mm) Ir-containing spot, despite the high propensity for hydrazine to decompose on the surfaces of the inlet system and vacuum chamber. (c) 2006 American Vacuum Society.