Immunohistochemical examination demonstrated expression of intercellular adhesion molecule-1 (ICAM-1) on 17 of 44 transitional cell cancers (TCCs) but not on normal transitional cells. ICAM-1 was frequently expressed in higher stage tumors, especially in those with abundant immune cells scattered within tumor. Analysis of infiltrating immune cells showed that they were composed mainly of T lymphocytes and a smaller number of macrophages bearing the lymphocyte function-associated antigen-1 (LFA-1). Expression of ICAM-1 on transitional cell cancer cell lines was augmented by in vitro treatment with interferon-gamma, tumor necrosis factor-alpha, and interleukin-1 beta. Furthermore, Northern blot analysis revealed higher quantities of a 3.3-kb RNA in T24 cells exposed to interferon-gamma or tumor necrosis factor-alpha. These results suggest that the expression of ICAM-1 on transitional cell cancers might be modified by cytokines produced by infiltrating immune cells, which might facilitate immune responses against cancer cells.