An ever-enlarging portion of hepatology research falls under the rubric of molecular biology. Thus, an attempt to summarize all molecular biology studies of liver disease in the past year is less than satisfying. One topic of particular significance relevant to molecular biology during the past year is the study of cytokines. Examples of these studies include: 1) the use of transgenic mouse models and other methodologies to study the effects of growth factors, especially transforming growth factor-α in liver regeneration and oncogenesis, 2) progress in studying the interactions between nonparenchymal cells and growth factors in liver processes, and 3) elucidation of the roles transforming growth factor-β and platelet-derived growth factor play in hepatic fibrogenesis.