Recently it has become clear that the inflammatory response of immune cells to target cells and extracellular matrix is regulated by several receptor-ligand molecules. Three main classes of molecules mediating intercellular adhesion and activation processes have been identified: the integrin, immunoglobulin and selectin families. This study surveys the expression of adhesion molecules on resident and infiltrating cells in human liver grafts. The patterns of cellular expression and inducibility in different pathological conditions of the graft are described. Our results show organ-specific regulation of the different adhesion molecules during alloreactive reactions and other types of inflammatory reactions. No rejection-specific patterns were detected on comparison with reperfusion damage or infectious transplant inflammation. Major differences were noted in the composition of the portal tract and sinusoid with regard to endothelial and parenchymal cell expression of cell-cell and cell-matrix adhesion molecules. Intravascular and interstitial differences in the expression patterns of leukocyte adhesion receptors support a concept of stepwise expression. The implications for the appearance of inflammatory reactions in human liver in immunosuppressive and therapeutic interventions are discussed. (HEPATOLOGY 1993;18:440–453).