Sulphur dioxide as a criterion of air pollution supresses macrophage functions. Some immunological changes in diabetes mellitus have been detected. In the present study, we examined the effect of sulphur dioxide on macrophage phagocytic activity in diabetic rats. The animals were separated into four groups as: 1) Control, 2) Sulphur dioxide, 3) Diabetes mellitus, 4) Diabetes mellitus+sulphur dioxide. The first and the third groups of animals were respirated with filtered atmosphere air in a special chamber one hour daily for eight weeks, while the other groups were exposed to 10 ppm sulphur dioxide in the same conditions and periods. The diabetic condition was induced in the third and fourth groups by administration of 5 mg/100 g bw alloxane. At the end of the experimental period, blood glucose levels significantly increased in the experimental groups compared to the control. While the phagocytic activity in peritoneal macrophages decreased in all experimental groups compared to the control. In conclusion, the supressive effect of sulphur dioxide on macrophage phagocytic activity increased the effects of diabetes.