Reactive sputtering of targets of certain noble (Au, Pt) and oxidizable metals (Co, Sn) are studied by glow discharge mass spectrometry (GDMS) and by x‐ray diffraction. It is concluded that (1) oxidation of the target occurs for Sn and Co, (2) a plasma reaction occurs for every metal, especially Au, and (3) a chemical decomposition of AuO and an oxidation to higher states occurs on the substrate for Pt, Co, and Sn.