The antidiabetic effect of clofibrate is well documented in the treatment of endogenous hypertriglyceridemia (HTG). Whether it is also effective in diabetic patients without HTG remains to be seen. 19 Type II diabetics without HTG (4 males, 15 females, age 61 +/- 21 years, duration of diabetes 9 +/- 6 years, body weight 118 +/- 20% according to Broca, triglycerides 140 +/- 156 mg/dl) were included in a randomised cross-over study and given a daily dose of 1.5 g clofibrate verum and clofibrate placebo, respectively, over 10 days while staying in hospital. The results showed that only in 8 patients under additional clofibrate therapy no changeover to insulin was required. Although blood glucose levels did not significantly improve, statistical evidence (as determined by the Grizzle analysis of variance) was given of an increased effect of sulfonylurea therapy. There was a negative correlation between the therapeutic effect and the individual blood glucose/insulin ratio following tolbutamide which was injected prior to the study. However, the incidence of insulin-demand was higher in patients with a high ratio than in those with a low ratio. Therefore, the specific antidiabetic effect of clofibrate seems to be only of minor clinical significance.