Postprandial hyperglycemia and elevations in glycated hemoglobin A1c (HbA1c) levels have been associated with long-term complications of diabetes. Because not all patients with type II, or non-insulin-dependent diabetes mellitus (NIDDM), respond adequately to diet, exercise, or treatment with oral sulfonylurea drugs, alternate therapies have been investigated. Acarbose, the first alpha-glucosidase inhibitor available in the United States, exerts its activity in the gastrointestinal tract. By reversibly inhibiting the enzymatic cleavage of complex carbohydrates to simple absorbable sugars, treatment with acarbose results in a reduction in postprandial blood glucose and, subsequently, reductions in HbA1c levels. Acarbose may be given as monotherapy with diet or in combination with diet and a sulfonylurea drug. The results of several controlled clinical studies conducted in the United States are reviewed here. Acarbose, in doses of up to 100 mg three times daily for periods of up to 16 weeks, was statistically significantly superior to placebo with respect to the mean reduction in HbA1c levels and mean 1-hour postprandial glucose levels. Adverse events were nonsystemic and primarily gastrointestinal in nature. Acarbose represents a new approach to the management of NIDDM, modulating gastrointestinal carbohydrate metabolism to control postprandial hyperglycemia and to maximize long-term glycemic control.