To evaluate the hypoglycemic effect of combination therapy with sulfonylurea and metforinin in NIDDM patients were have compared the blood glucose levels before and after combination therapy m 62 NIDDM patients. The results were as follow; 1) The mean fastig blood glucose level with sul- fonylurea only was 204 +-43 mg/dl and that with combination therapy was 138+-43mg/dl (p<0.001). The mean postprandiel glucose level with combination therapy was also decreaed significantly. 2) In 8 patients, the mean fasting glucose level with combination therapy was 127+-18mg/dl and that with rnetformin only was 200+-26mgfd) (p<0.001). 3) The fasting blood iosulin levels sheed no significant difference between therapy with combination and with sulfonylurea only. 4) Combination therapy showed no significant side effect. Only mild gastroinkestinal symptoms were observed. From above results, we concluded that combination therapy with sulfonylurea and metformin is one of usefu1 methods to treat NIDDM patients with sulfonylurea failure.