Positive ion sampling measurements have been conducted on dc discharges containing 0.33% and 1.2% SO2 in He. Ions from SO2 include S+, O+, O2+, SO+, SO2+, and SO3+. Studies were made of the functional dependencies on gas pressure and discharge current. Interpretation of these results led to the conclusion that appreciable dissociation of SO2 occurred within the discharge. This hypothesis was confirmed by sampling the neutral gas components with and without a discharge. Measurements show the degree of dissociation increases with discharge current and reaches a limiting value which is relatively constant over the pressure range studied. For 1.2% SO2 in He, the degree of dissociation can become as large as 80% at 6.5 Torr and for a 20-mA discharge current. The results moreover suggest that an appreciable fraction of the dissociated particles is in the form of SO.