Types I, III, IV, and AB collagens have been extracted from human cirrhotic livers and specific antibodies have been raised in rabbits and purified. Histological immunofluorescent staining of collagen types in normal and fibrotic human livers reveals the respective distribution of the various collagens among the hepatic connective matrix and the modification of the normal pattern in fibrosis: types I and III appear to be the main components of the fibrotic connective matrix in enlarged portal spaces and of the Dissian reticulin framework; type IV collagen deposits are thickened around portal vessels and ducts and outline lobular capillarized sinusoids; type AB collagen appears as thin punctual deposits in portal and Dissian fibrotic connective matrix. Ultrastructural immunoperoxidase labeling of type I and III collagen makes it possible to identify the typical collagen fibers, using 65 nm periodicity, as type I collagen and the fibrillar associated network as type III collagen. Fibers of type I collagen are preferentially organized in large dense bundles in Dense Connective Matrix Organization (DCMO), since fibrillar type III collagen network is predominant in Loose Connective Matrix Organization (LCMO) surrounding vascular and biliary tracts.