Owing to the presence of hyperlipoproteinemia IIa, twelve patients without gallstones were treated daily with 20 mg, 40 mg and 80 mg of Lovastatin, each dose being administered for 4 weeks. At the conclusion of each 4-week treatment phase, bile was obtained from the fasting patient following injection of 5 micrograms ceruletid i.v. with the aid of a duodenal tube. The long nucleation time of bile was not shortened by the therapy. The bile cholesterol saturation index showed a decline with Lovastatin, which was particularly obvious in patients with an initially oversaturated bile. In contrast to other lipid-reducing agents (e.g. fibrates), Lovastatin does not lead to increased lithogenesis of the bile, but may in certain circumstances have an prophylactic effect against the formation of gallstones.