The effect of acarbose, an alpha-glucosidase inhibitor, on postprandial glucose and lipid metabolism was investigated in patients with type 2 diabetes mellitus. Twenty patients (10 men and 10 women) with type 2 diabetes mellitus were studied. A test meal was taken with or without 100 mg of acarbose. The levels of plasma glucose, and serum immunoreactive insulin, lipids, apolipoproteins, and remnant-like particle cholesterol were investigated. Acarbose inhibited the postprandial increase of both plasma glucose and serum immunoreactive insulin. Acarbose also significantly suppressed the increase of serum triglycerides at 60, 90, and 120 min (P < 0.05 to P < 0.01), and the increase of serum remnant-like particle cholesterol at 60 and 120 min (P < 0.05). Acarbose inhibited the postprandial decline of apolipoprotein C-II, and decreased the postprandial serum apolipoprotein C-III level. These results suggest that acarbose may improve postprandial hyperlipidemia as well as postprandial hyperglycemia in patients with type 2 diabetes mellitus.