Silymarin (SIL), a standardized plant extract containing about 60% of the polyphenol silibinin, is used as a hepatoprotective agent. In order to explore the effect of SIL on liver cell regeneration in a model of progressive biliary liver fibrosis this substance was applied to adult Wistar rats that were subjected to complete bile duct occlusion (BDO) by injection of the sclerosant sodium amidotrizoate (ethibloc(R)). Rats with sham-operation that received SIL at an oral dose of 50 mg/kg per day (n = 10) and rats with BDO alone (n = 20) served as controls, whereas groups of 20 animals were given SIL at a dose of 25 and 50 mg/kg during weeks 1-6 or of 50 mg/kg during weeks 4-6 of BDO. Animals were killed after 6 weeks. Except for a lower liver weight, total collagen content and histological fibrosis score in the groups that were treated with SIL at 50 mg/kg over 3 or 6 weeks, the number, size and mitotic rate (per microscopic field) of hepatocytes was not different among all groups with BDO. We conclude that SIL had only a minor (macroscopic) effect on the parenchymal compartment, (C) 1998 John Wiley & Sons, Ltd.