Aldrich's pure ZrO2, BET sp. surface 29 m(2)/g, was studied (A) fresh; (B) calcined 773 K, impregnated with aq. H2PtCl6, kept 48 h/373 K, dehydrated, dried 378 K/8 h, and reduced in H, at 773 K. Mass spectra disclosed Zr+, ZrO+, and ZrO2+. on the surface of A and B, thus showing the ZrO2 surface to remain chemically unaffected by calcination. Crystallites, 35-40 nm, were evident. The 5%Pt/ZrO2 catalyst showed neg. spectra with ZrO- and ZrO2- Pt-, PtCl-, PtClO- and PtCl2-, and the less intense pos. spectra with Pt+, PtO+ PtCl+, PtClO+ and PtCl2+, indicative of Pt-Cl bondings retained from H2PtCl6. The surface was homogeneous, Pt was highly dispersed and partly aggregated (phi, 8 mum).