Adhesion molecules appear to play important roles in vascularized organ allograft rejection, because antibodies directed against them are effective in prolonging survival of vascularized organ allografts in rodents. However, the efficacy of these agents for cellular allografts is unknown. The current studies were undertaken to determine the role of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) on host immune responses to purified hepatocytes. Host mice (C3H, H-2k) grafted with hepatocytes in sponge matrix allografts (HC-SMA) received IgG isotype control, anti–ICAM-1, or anti–VCAM-1 monoclonal antibody (mAb) on days 0 through 9 after grafting. Twelve to 14 days later, host cells infiltrating the HC-SMA were assessed for the development of allospecific cytolytic T cells (allo-CTLs). Treatment with anti–ICAM-1 or anti-VCAM-1 mAb resulted in significantly decreased recruitment of host cells into HC-SMA (P < .035). However, only anti–ICAM-1 mAb resulted in abrogation of development of allo-CTLs in HC-SMA (P = .001). C3H (H-2k) hosts grafted with allogeneic hepatocytes from control C57BL/6 (H-2b) or ICAM-1 knockout [H-2b] mice elicited the development of allo-CTLs in HC-SMA (P = not significant). Furthermore, there was no difference in the development of allo-CTLs in HC-SMA of control hosts [C57BL/6, H-2b] compared with ICAM-1 knockout hosts (H-2b) (P = not significant). Treatment with anti–ICAM-1 mAb had no effect on the development of allo-CTLs in ICAM-1 knockout (H-2b) hosts bearing HC-SMA. The immunosuppressive effect of host treatment with anti–ICAM-1 mAb does not appear to be a consequence of simple blockage of donor hepatocyte or host immune cell expression of ICAM-1, but suggests a potential inhibitory effect on host immune cell activation or function, as well as an effect on recruitment of host cells to the allograft.