Acarbose delays digestion of complex carbohydrates and disaccharides to absorbable monosaccharides, by reversibly inhibiting alpha-glucosidases within the intestinal brush border, thereby attenuating postprandial blood glucose peaks. Clinical trials have demonstrated that acarbose generally improves glycaemic control in patients with non-insulin-dependent diabetes mellitus (NIDDM) managed with diet alone, or with other antidiabetic therapy, as evidenced by decreased postprandial plasma glucose and glycosylated haemoglobin levels. It does not appear to directly alter insulin resistance, but may lower postprandial plasma insulin levels. Fasting plasma glucose, triglyceride and/or cholesterol levels may also be decreased. Acarbose also improved metabolic control in patients with insulin-dependent diabetes mellitus (IDDM), frequently decreasing insulin requirements, although further studies are required in this indication. Improved metabolic control appears to delay or prevent long term vascular complications of diabetes, and indeed, acarbose appeared to inhibit development of such complications in preliminary animal studies, but this finding requires confirmation in clinical studies. While acarbose seldom causes systemic adverse effects, it is associated with a high incidence of gastrointestinal disturbances such as flatulence, abdominal distension, borborygmus and diarrhoea, caused by fermentation of unabsorbed carbohydrates. However, these symptoms tend to subside with continued treatment and adherence to an appropriate diet. Thus, acarbose appears to be a worthwhile adjunctive therapeutic option for patients with NIDDM inadequately managed by diet alone, or with pharmacological therapy, and possibly also for patients with IDDM. However, further long term efficacy and tolerability data are required, particularly in the latter indication.