Immunohistochemical techniques were used to confirm biochemical evidence that parenchymal cells isolated from adult rat liver and maintained in nonreplicating monolayer culture for 2 days synthesized type IV basement membrane collagen. On continued incubation in serum-free medium, the hepatocytes also synthesized the interstitial collagens, types I and III. Consistent with these results in culture, type IV collagen was localized to the hepatocytes in slices of pathologic rat liver. Hence collagen formation is a previously unrecognized function of the hepatocyte that may be important in the pathogenesis of liver fibrosis or cirrhosis.