The hypoglycemic and weight reduction effect of metformin, derivatives of kiguanicle, were studied on 51 non-insulin dependent diahetes mellitus patients registered at the Diabetes Clinic of Yonsei Medical Center.observing the effect after administrating the during for 1-3 months to these patients, the following results were obtained. 1) FBS decreased from 219. 2+-53,7 mg/dl to 135.9+-16,3 rng/dl after treatment with merformin, 1.2+-0.4 g/ day, for 6,3+-2.1 days, 2) In 1 and 3 month follow up periods, fair control of FBS (<160mg/dl) were achieved in 21 (62%) and 15 patients (83%) among 34 and 18 patients respectively, 3) The weight reduetion from admission was 3. 2+-2.2% after induction periods, and 4.1+-3 6% and 6.1+-4. 5% after 1 and 3 month follow up periads eaeh. 4) A.ccording to our results, differences in the duration of disease resulted in a certain influence on the effect of treatment. The ahorter the duratirn or' disease, the better the results. 5) As the side effect, loss of appetite (19.6%), nausea (15 7%), diarrhea (13. 7%) abdominal dis- comfort (7 8%) or increased anion gap (2.0%),alI transient and mild, were seen in 17 patients (33%) but lactic acidosis was not seen. This results suggest that metformin coupled with diet and exercise was proved tu be an useful therapeu- tic regimen to the patients with NIDDM especially obese type despite of a mild and transient side effects.