An 88-year-old woman patient had received 250 mg. of chlorpropamide daily for two weeks as a substitute for insulin therapy. When the blood sugar level was found to be 220 mg.%, the dosage was increased to 250 mg. twice daily. After one day, the patient was hospitalized in coma but was released from the emergency room after apparent complete recovery. On the next morning, she was again hospitalized in deep coma and the blood sugar level was 31 mg.%. The next morning it was 8 mg.%. Dramatic recovery was brought about by intravenous administration of dextrose and supplementary feedings. It would appear mandatory that patients receiving chlorpropamide be kept under close clinical observation, with frequent blood sugar level determinations.