The aim of this double-blind, placebo-controlled, multinational, five-arm study was to investigate the dose-response relationship of acarbose as a first-line drug in the treatment of type 2 diabetes (non-insulin dependent) over a range of minimal and maximal doses according to the European recommendations. The study included 495 patients from 7 countries who were insufficiently controlled with diet alone (glycosylated haemoglobin HbA1C 6.5%-9%). Acarbose, 25, 50, 100 or 200 mg t.i.d., or placebo t.i.d. was given for 24 weeks. Even a low dosage of 25 mg t.i.d. acarbose reduced fasting and postprandial blood glucose levels (1 h postprandial -11.6%; 2 h postprandial -11.3%). Acarbose in a dosage of 200 mg t.i.d. had the greatest effect on these parameters. In the placebo group the mean 2 h postprandial area under the curve (AUC) value for blood glucose was 22.6 mmol/l after 24 weeks' therapy. The mean 2 h postprandial AUC values in the patients given acarbose at doses of 25, 50, 100 and 200 mg t.i.d. were found to be 21.2, 19.6, 20.3 and 18.5 mmol/l, respectively. The corresponding HbA1C values for the placebo and acarbose groups were 7.83%, 7.37%, 7.08%, 6.98% and 6.79%. Interestingly, there was a plateau of blood glucose level at a dosage of 50-100 mg t.i.d. The frequency of flatulence decreased with the duration of drug therapy, but we could not find a linear relationship between doses of acarbose and the gastrointestinal side effects. Less than 3% of patients stopped tablet intake due to adverse events.