We show that in two cell lines of human squamous cell carcinoma (SCC) which slightly express intercellular adhesion molecule-1 (ICAM-1), the expression is enhanced not only by interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) but also by interleukin-1 (IL-1) and lipopolysaccharide (LPS). This expression is totally dependent on the increase of ICAM-1 mRNA. This evidence contrasts with previously reported findings indicating that, in human cultured keratinocytes, ICAM-1 expression is induced by IFN-gamma and TNF-alpha, and not by either IL-1 or LPS. This result suggests that various cytokines or agents easily enhance ICAM-1 expression in SCC cell lines, and may explain the clinical finding that ICAM-1 expression increases according to the progression of malignant tumors.