ICAM-1 is an inducible cell surface protein that is involved in cell extravasation into inflamed tissues as well as immune responses. ICAM-1 expression is upregulated by proinflammatory cytokines such as TNF-α and IL- 1β in numerous cell types including the astrocyte, which functions as an immune effector cell in the central nervous system (CNS). We investigated the mechanism by which the ICAM-1 gene is transcriptionally regulated in astrocytes in response to TNF-α and IL-1β. Human ICAM-1 promoter constructs linked to the reporter gene luciferase were transiently transfected into astrocytes, stimulated with TNF-α and IL-1β, and ICAM-1 promoter activity examined. We determined that binding sites for both NF-κB (-186 bp region) and C/EBP (-198 bp region) are involved in TNF-α and IL-1β-mediated ICAM-1 upregulation. Electrophoretic mobility shift assays using antibodies against NF-κB and C/EBP isoforms showed that p65 homodimers and p65/p50 heterodimers bind to the NF-κB site, and C/EBPδ homodimers and C/EBPβ/δ heterodimers bind to the C/EBP site. Transient transfection assays demonstrated that overexpression of p65 could transactivate the promoter activity of ICAM-1 reporter constructs. p50 overexpression had no effect on the basal levels of ICAM-1 transcription, but inhibited, in a dose dependent manner, p65 mediated transcription. Overexpression of C/EBPβ slightly inhibited basal levels of ICAM-1 promoter activity, however, when C/EBPβ and p65 were cotransfected, C/EBPβ completely abolished the transactivating effects of p65. These results demonstrate that cytokine-induced ICAM-1 expression in astrocytes is regulated by interactions between NF-κB and C/EBP transcription factors.