Previous observations on 62 obese diabetic patients showed that phenmetrazine hydrochloride significantly reduced appetite and weight. In the present study 30 obese diabetic patients were divided into two groups. Each patient received 25 mg. per day of either phenmetrazine hydrochloride or diethylpropion under "double-blind" conditions. Group A (14 patients) lost, on the average, 6.71 lb. (3.05 kg.) during an initial six-week phenmetrazine period and 1.37 lb. (0.62 kg.) during the subsequent six-week diethylpropion period. Group B (16 patients) lost 2.77 lb. (1.26 kg.) during their initial six weeks of taking diethylpropion and 3.44 lb. (1.56 kg.) during the subsequent six-week phenmetrazine period. Both drugs were significantly anorexigenic; but in the dosages used, phenmetrazine caused both greater weight-loss and a higher incidence of side-effects.