Acarbose is an alpha-glucosidase inhibitor proposed for the treatment of diabetic patients. It acts by competitively inhibiting the alpha-glucosidases in the intestinal brush border. The principal action of these enzymes is to convert nonabsorbable dietary starch and sucrose into absorbable monosaccharides (e.g. glucose). Enzyme inhibitors delay this conversion, slowing the formation and consequently the absorption of monosaccharides, and thus reducing the concentration of postprandial blood glucose. Both starch and sucrose are influenced, whereas lactose and glucose are not. Many studies in experimental animals, healthy volunteers and patients with non-insulin-dependent diabetes mellitus (NIDDM) have shown that acarbose decreases postprandial blood glucose, with a lesser reduction of fasting blood glucose, plasma triglycerides and postprandial insulin levels. In long term studies in NIDDM patients, acarbose significantly reduced glycosylated haemoglobin levels. Acarbose is only minimally absorbed from the gut and no systemic adverse effects have been demonstrated after long term administration. The drug allows undigested carbohydrates to pass into the large bowel where they are fermented causing flatulence, bloating and diarrhoea. These symptoms, which occur in approximately 30 to 60% of patients, tend to decrease with time and seem to be dose-dependent. They are minimised by starting therapy with low doses (such as 50mg 3 times daily) which may be effective in many patients. An increase in serum hepatic transaminases observed in earlier studies in the US, where doses of acarbose up to 900mg daily were used, has been not reported with the lower doses of the drug actually recommended [150 to 300mg (up to 600mg) daily]. In conclusion, acarbose may be useful in patients with NIDDM when diet alone is no longer able to maintain satisfactory blood glucose control. Furthermore, it may be a valid alternative to sulphonylurea or biguanide therapy when these drugs are contraindicated and insulin administration may be delayed. Acarbose seems also to be a useful adjunct to hypoglycaemic oral agents but its precise role in this field has not been fully clarified.