Male F-344 rats were treated for 10 weeks either with CCl4 (0.2 ml/kg, per os, twice a week) or with CCl4 (same as above) and phenobarbital (0.2 g/l in drinking water). Liver fibrosis and cirrhosis developed in both treated groups, and was confirmed histologically. Cirrhosis was more frequent after the CCl4 + phenobarbital treatment. The collagen content of the liver, measured by morphometry and biochemically, was significantly higher in the animals of the group treated with CCl4 + phenobarbital than in the animals treated only with CCl4. Specially altered fat-storing cells (Ito cells) were found in the periportal and septal fibrotic areas in direct proportion to the amount of fibrosis and cirrhosis. They were identified as altered fat-storing cells by their desmin content and Vitamin A storing capability. This study demonstrated that these cells were enlarged and contained neutral fat, lipofuscin and PAS-positive material. The potential role of GAG-containing FSC in fibrogenesis is discussed.