Mass spectrometric measurements have been made of the ions present in rf discharges of argon and argon containing small concentrations of cesium. Data were obtained for normalized argon and cesium pressures up to 3 and 4×10−3Torr, respectively. The relative ion singals are functions not only of the argon and cesium concentrations but also of the plasma excitation power. For argon‐cesium mixtures the primary ions that are observed are Ar+, Ar2+, and Cs+. Analysis of the data for Ar+and Ar2+suggests that Ar2+is produced by both Hornbeck‐Molnar and three‐body conversion processes. Interpretation of the results leads to the conclusion that in the present study Cs+is formed by both direct ionization and by collisions of argon metastables with neutral cesium.