Several adhesion molecules including intracellular adhesion molecule‐1 (ICAM‐1) are expressed by astrocytes, the predominant glial cell of the central nervous system (CNS). Such molecules are important in the trafficking of leukocytes to sites of inflammation, and in lymphocyte activation. ICAM‐1 is constitutively expressed by neonatal rat astrocytes, and expression is enhanced by the proinflammatory cytokines interleukin‐1β (IL‐1β), tumor necrosis factor‐α (TNF‐α), and interferon‐γ (IFN‐γ), with IL‐1β and TNF‐α being the strongest inducers. In this study, we have examined the nature of the second messengers involved in ICAM‐1 gene expression induced by the cytokines IL‐1β and TNF‐α. Our results indicate that stimuli related to protein kinase C (PKC) such as the phorbol ester phorbol 12‐myristate 13‐acetate (PMA) and calcium ionophore A23187 increase ICAM‐1 mRNA expression, whereas cyclic nucleotide analogs and PKA agonists have no effect. Pharmacologic inhibitors of PKC such as H7, H8, and calphostin C inhibit ICAM‐1 gene expression inducible by IL‐1β and TNF‐α. Prolonged treatment of astrocytes with PMA results in a time‐dependent downregulating of the PKC isoforms α, δ, and ϵ, and a concomitant diminution of ICAM‐1 mRNA expression induced by IL‐1β, TNF‐α, and PMA itself at specific time points post‐PMA treatment. These data, collectively, demonstrate a role for various PKC isoforms in IL‐1β and TNF‐α enhancement of ICAM‐1 gene expression in rat astrocytes. © 1995 Wiley‐Liss, Inc. Copyright © 1995 Wiley‐Liss, Inc.