AbstractMonoclonal antibody RR1/1 directed against the putative LFA‐1 ligand molecule intracellular adhesion molecule‐1 (ICAM‐1) was found to inhibit the T cell prolifera‐tive response to the antigen PPD. Interestingly, the percentage of unstimulated monocytes which expressed ICAM‐1 on their surface appeared to vary greatly from person to person although the majority of monocytes did express high levels of ICAM‐1 within their cytoplasm and surface expression could be rapidly induced on most cells by adherence to fibronectin. Resting T cells showed no evidence of surface or cytoplasmic ICAM‐1 although expression was induced both within the cell and on the membrane as a result of activation with phytohemagglutinin or a combination of OKT3 and phorbol 12, 13‐dibutyrate. The significance of these findings with respect to the function of monocyte and T cell in the generation of an immune respo