The effects of alpha-glucosidase inhibitor (acarbose) were studied in 36 patients with non-insulin-dependent diabetes mellitus (NIDDM), aged 34-67 years with a mean duration of diabetes of 8.8 +/- 0.9 years. They were poorly controlled with diet plus sulfonylurea alone or plus sulfonylurea combined with metformin drugs. Acarbose, 100 mg three times daily, was additionally given to these patients for six months. Results showed small but significant decreases (P < 0.001) in postprandial blood glucose level. Glycosylated hemoglobin level was lowered significantly (P < 0.001) and was normalised (level of < 8%) in 17 per cent of the patients. Fasting serum triglycerides level decreased significantly (P < 0.01), whereas, no significant changes in serum total cholesterol and HDL cholesterol levels were seen. Body weight also decreased significantly (P < 0.001) at the end of acarbose trial. Flatulence was the major side effect of acarbose found in 42 per cent of the patients but it was well-tolerated and may be transient and self-limited. We concluded that the addition of acarbose to the therapeutic regimens of diet therapy plus sulfonylurea or plus sulfonylurea combined with metformin drugs led to significant improvement of glycemic control. Acarbose may be a safe and valuable adjunct to diet and sulfonylurea and metformin treatments in obese, poorly-controlled patients with NIDDM.