The effects of four different doses of ursodeoxycholic acid (250, 500, 750, and 1000 mg daily) on biliary lipids were studied in 24 patients with radiolucent gallbladder stones. There was a significant increase in the proportion of ursodeoxycholic acid in bile after all doses, being greatest with 750 and 1000 mg daily. Unsulphated lithocholic acid was also increased in the bile after therapy, while the other major bile acids were reduced. The cholesterol content of bile was reduced by all doses, and this change was most marked after 1000 mg (from 10.9 +/- 1.4 to 5.6 +/- 0.5 mol%, P < 0.01). Biliary cholesterol saturation improved significantly only after 750 and 1000 mg daily.