Female non-insulin-dependent diabetics have a high prevalence of gallstones. Treatment of hyperlipidaemia in these patients may modify the risk. Seventeen female non-insulin-dependent diabetics (age 35-65) were treated with simvastatin (n = 10) or bezafibrate (n = 7) and had the cholesterol saturation index (CSI) of bile and gall-bladder emptying measured before and after 3 months therapy. In both groups, there was a significant reduction in serum cholesterol following treatment. The mean pretreatment cholesterol saturation indices of bile did not differ between the two groups but, after 3 months therapy, there was a highly significant difference in CSI between the bezafibrate group (2.0 +/- 0.33) and the simvastatin group (1.1 +/- 0.14) P < 0.002. Whereas the increase in the CSI (42%) observed with bezafibrate therapy was significant, the decrease in the simvastatin group (14%) was only significant in those whose pretreatment cholesterol saturation indices were elevated. Despite the differences in CSI observed between the two treatment groups, no changes in gall-bladder emptying were detected.