Intercellular adhesion molecule-1 (ICAM-1) has recently been identified as one of the ligands for lymphocyte function-associated antigen-1 (LFA-1). Immunohistochemical staining of frozen tissue sections using the ICAM-1 antibody RR1/1 demonstrated significant levels of ICAM-1 expression on human glioblastoma cells and on intratumoural vascular endothelial cells. ICAM-1 was weakly expressed or absent from low grade gliomas and absent from normal and fetal brain. ICAM-1 expression was similar to that of MHC class II, HLA-DR antigens. Glioblastoma cell lines constitutively expressed ICAM-1 to a minimal or moderate extent. Surface antigen expression of ICAM-1 and ICAM-1-specific mRNA could be significantly increased by incubating glioblastoma cells with interleukin-1β (IL-1β), tumour necrosis factor-alpha (TNF-α), and interferon-gamma (IFN-γ). IL-2, IL-4, IL-6 and transforming growth factor β2 (TGF-β2) had no significant effect on surface antigen expression. Significant enhancement of ICAM-1 expression was obtained using TNF-α and IL-1β at 1-10 U/ml and at 500 U/ml of IFN-γ. Induction of ICAM-1 specific mRNA was observed 4 h after cytokine treatment and decreased by 24 h. Surface antigen expression of ICAM-1 increased for up to 48 h after treatment.