Serum laminin (P1 fragment) and type IV collagen levels were determined in patients with hepatic disorders. The method was based on a sandwich enzyme-immunoassay using two monoclonal antibodies that recognize different epitopes of either laminin or type IV collagen molecule. Laminin and type IV collagen levels in the serum of patients with chronic hepatic disorders were higher as compared with those in healthy control subjects, with the increment of serum type IV collagen being far greater than that of laminin. Since type IV collagen and laminin are major basement membrane components, it is suggested that the higher levels of these peptides may reflect a so-called capillarization of the perisinusoidal wall encountered in hepatic fibrogenesis. The assay system used in this experiment is simple and sensitive and can be applied to clinical evaluation of hepatic fibrosis.