This study documents the hepatic morphology and the ultrastructure of a model of hepatic fibrosis in rabbits. Rabbits were given a cholesterol- supplemented diet (1%), a stilbestrol diet (10 mg subcutaneously twice a week), or both treatments simultaneously for 7 weeks. Rabbits given the combined treatment developed sinusoidal and portal fibrosis with only a mild disturbance of acinar vascular relationships. Ultrastructurally, there was marked widening of the spaces of Disse by collagen fibers, basement membrane material adjacent to endothelial cells and hepatocytes, blunted hepatocellular microvilli, activated stellate cells, lipid droplets in endothelial cells and hepatocytes, and degranulated platelets in sinusoids. The hepatic hydroxyproline content was markedly increased (12.0 ± 5.2 vs. 4.8 ± 1.5 mmol/g of liver dry weight; P < .001). Plasma bile acids were markedly increased (222 ± 180 vs. 12 ± 5 in controls; P < .001). Dipyridamole (25 mg every 12 hours) that was given in addition to cholesterol and stilbestrol decreased the hepatic collagen content (-49% and -48%, in two experiments; P < .05 in both) and splenomegaly. This model provides a reliable method for the production of extensive sinusoidal fibrosis with capillarization of sinusoids. Hepatocellular degeneration is only mild to moderate, and fibrosis occurs slowly without the sudden pathological changes that occur with other models of hepatic fibrosis, such as with the administration of CCl4 or galactosamine. The mechanism of injury may involve the accumulation of bile salts or the generation of free radicals from cholesterol oxidation products. The possibility that the sinusoidal release of platelet-derived factors may have a role in the activation of stellate cells (lipocytes) is supported by the suppression of fibrogenesis by dipyridamole.