The immunohistological localization of components and neoantigens of the C5b-9 human terminal complement complex was studied in 30 human liver biopsies. C5b-9, apparently in the soluble SC5b-9 form, was invariably detected in normal liver capsule and normal portal tract connective tissue. In livers with fibrosis and or cirrhosis, the pathological connective tissue contained variable amounts of SC5b-9 which was distributed in a similar way to that seen in normal livers. There was no significant C5b-9 deposition outside of the portal tract and capsule in any of the liver biopsies. In particular, in pathological livers, there was no deposition in relation to cellular infiltrates or areas of hepatic necrosis. These data support the concept that C5b-9 is a common component of connective tissue but do not indicate that C5b-9 mediated pathways are involved in the pathogenesis of hepatic injury.