alpha-Glucosidase inhibitors such as acarbose improve blood glucose control in diabetes by delaying or reducing carbohydrate absorption. The fermentation of malabsorbed carbohydrate in the colon is associated with the production of gas, leading to flatulence, and short chain fatty acids such as acetate, which may have systemic effects. To see if acarbose raised fasting serum acetate in diabetic patients, we studied 85 subjects selected from the 267 who had completed a 1-year, double-blind, placebo-controlled, parallel design study of the effects of acarbose in the treatment of diabetes. At baseline, there was no significant difference between the 44 subjects subsequently randomized to placebo and the 41 randomized to acarbose, respectively, in fasting serum acetate (80 +/- 5 vs 71 +/- 4 mumoll-1) or glycosylated haemoglobin (HbA1C; 7.2 +/- 0.3 vs 7.4 +/- 0.3%). Compared to placebo, acarbose treatment significantly increased fasting serum acetate by 11 +/- 4 vs 2 +/- 3 mumoll-1 (p < 0.02) and reduced HbA1C by -0.59 +/- 0.16 vs -0.13 +/- 0.20% (p < 0.02). Acarbose treatment had no significant effect on serum cholesterol or non-esterified fatty acids, but was associated with a significant increase in flatulence. There was no relationship between changes in serum acetate and changes in HbA1C, serum cholesterol or symptoms. We conclude, in subjects with diabetes who tolerate therapy for a 1-year period, that acarbose treatment increases serum acetate. The magnitude of change in acetate was unrelated to side-effects or changes in blood glucose control or serum lipids.