3-hydroxy,3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors reduce biliary cholesterol saturation index (CSI) in duodenal bile in hypercholesterolemic patients and might be useful for gallstone dissolution. However, preliminary data suggest that these drugs are not effective in this respect. We therefore studied 33 patients with radiolucent gallstones in an opacifying gallbladder who were scheduled for elective cholecystectomy. Patients were treated with 40 mg pravastatin day or placebo during the 3 weeks before surgery. Six patients could not be evaluated. Baseline characteristics (age, sex, body mass index, serum cholesterol, and the solitary/multiple gallstone ratio) were similar in both groups. Serum cholesterol fell by 3% in the pravastatin group (P < .001) and remained unchanged in the placebo group. Biliary cholesterol (9.5 i-1.3 vs. 14.3 ? 1.5 mmoyL, P = .026), and phospholipid concentrations (24.8 ? 3.9 vs. 36.7 2 3.9 mmol/L, P = .043) were lower in the pravastatin group. Although bile salt concentrations were lower in the pravastatin group (114 i-21 vs. 152 ? 15 mmovL), this difference was not significant. CSI was not different between both groups (142 2 27% [pravastatin] vs. 113 ? 6% [placebo], P = NS). Cholesterol crystals were present in fresh bile in 7 of 13 patients in the pravastatin group and in 11 of 14 controls (P = NS). Nucleation time was comparable between the 2 groups (13 ? 3 vs. 9 -t-3 days, P = NS). Bile salt species and