In hepatocellular carcinoma, there is modification of cell-to-cell and cell-to-extracellular matrix interactions. Two cases of well-differentiated hepatocellular carcinoma that developed in noncirrhotic livers were explored by light and electron microscopy on perfusion-fixed liver biopsy specimens. In addition, immunocytolocalization of collagen types I, III, and IV, laminin, and fibronectin was assessed. The main features included the following: absence of collagen staining inside the tumor with Sirius red; decrease of collagen types I and III and the increase of collagen type IV, laminin, and fibronectin; widening of Disse's spaces containing numerous, discontinuous, and thick fragments of basement membrane-like material piled up beneath endothelial cells and around perisinusoidal cells; transformation of perisinusoidal cells into cells with the characteristics of fibroblasts and myofibroblasts; decreased numbers of fenestrae for endothelial cells with processes often overlapping and attached with tight junctions; and rarefaction of Kupffer's cells. Expression of cellular and extracellular material abnormalities are related to the tumor differentiation. The study of these abnormalities may have implications in prognosis.