Tolazamide, a new oral hypoglycemic agent, was compared with tolbutamide, a related chemical compound, for stability of control of 12 patients suffering from maturity-onset diabetes mellitus. A short 12-week study was conducted which incorporated a cross-over design and the results were examined by variance analysis after dosage was individualized to the patient''s requirements. Greater stability of fasting blood sugar was found on tolazamide; patients also had less glycosuria and lower fasting blood sugar on tolazamide. Tolazamide appeared to be between 5 and 6 times as potent as tolbutamide, mg. for mg. No hepatic, renal, hematologic or symptomatic toxic reactions were observed during the total of 72 person-weeks of tolazamide therapy.