TGF-beta 1 is a potent inhibitor of hepatocyte proliferation in vivo and in culture and an inducer of fibrogenesis. It is produced by non-parenchymal cells in normal, regenerating, neoplastic and pre-neoplastic liver. TGF-beta 2 and beta 3 are also found in liver non-parenchymal cells and the amounts of their mRNAs increase during liver regeneration. TGF-beta 2 has similar effects to TGF-beta 1. Membranes from normal adult rat liver bind TGF-beta 1 with kinetics consistent with the presence of a single high affinity binding site; membranes from livers that have been regenerating for 12-72 hours show high affinity binding sites not detected in livers of normal or sham-operated rats. Affinity labelling of membranes from normal and regenerating liver shows two receptor proteins with Mr 85,000 and 65,000. In contrast, a prominent band corresponding to a binding protein of Mr 280,000 is detected in membrane preparations of cultured liver epithelial cells. Although modulation of TGF-beta 1 receptors occurs during liver regeneration, it has not been possible to determine which receptor is responsible for the TGF-beta 1 effects in hepatocytes. Other studies have demonstrated a significant correlation between TGF-beta 1 mRNA expression and various indicators of fibrogenesis in patients with chronic liver disease. Thus in animals and humans TGF-beta 1 appears to play a major role in the pathogenesis of fibrosis in chronic liver disease.