Mass spectrographic studies have been conducted on the positive ions and neutral species of glow discharges containing 1.0 pct so2 and 1.0 pct CO in helium. Measurements were conducted for gas pressures from 3.5 to 10.1 Torr using both DC and 60-hz ac excitation. The ion species that were observed included s+, so+, so2+, o+, o2+, c+, co+, and co2+ with less amounts of so3+, (co)2+, sco+, and (so.Co)+ or cs2+. Interpretation of the functional dependence of the various ionic and neutral species on pressure and applied power showed that CO reacted with the so formed in the discharges to produce co2 and sulfur. Deposition of elemental sulfur was observed in the plasma container.