The results of chlorpropamide treatment of 100 diabetic patients observed for up to one year are recorded. The average initial dosage was 500 mg. and maintenance dosage 250 mg. The following conclusions are drawn: 1. Chlorpropamide is a potent antidiabetic compound capable of producing hypoglycaemic symptoms. In the present series it gave a good or excellent response in 71 per cent, of diabetic patients. With better co-operation a further 10 per cent, would have had similar control. 2. The main contraindication to this form of treatment irrespective of the patient’s age is the presence of ketonuria without infection. Disordered fat and glucose metabolism in “ juvenile type ” diabetes requires insulin treatment. 3. Severe obesity tends to produce refractoriness to chlorpropamide. 4. Weight gain in responsive patients is common and does not depend only on the diet. 5. No significant difference of response in the sexes was observed. 6. Toxic reactions sufficient to stop treatment occurred in two patients, one suffering allergic erythema and the other leucopenia. One patient had minor digestive upset. Reference is made to the literature regarding the results obtained by other workers and the incidence of toxic effects. Evidence from the literature relating to an anti-ketotic effect from chlorpropamide is presented.