Interleukin-1 induced the expression of cyclooxygenase II in renal mesangial cells. This effect was similar to that seen by phorbol myristate accetate which also induced the message for COX II. Cycloheximide superinduced the message for COX II in the presence of IL-1beta. While the message for COX II when stimulated by PMA was completely inhibited by dexamethasone with concentrations of dexamethasone which inhibited PGE(2) formation, dexamethasone only partially inhibited the message for COX II by Northern analysis. Genistein, an inhibitor of tyrosine phosphorylation completely inhibited the ability of IL-1beta to induce the COX II message. Immunocytochemical studies confirmed the ability of IL-1beta to selectively induce the COX II protein without any effect on COX I protein. These studies confirm the dependency of tyrosine phosphorylation in the IL-1beta induced expression of COX II message and protein.