Treatment of rat mesangial cells with interleukin 1β (IL-1β) and forskolin greatly enhanced the expression of group II phospholipase A 2 (PLA 2 ) mRNA, with subsequent increased synthesis and secretion of PLA 2 as detected by PLA 2 activity measurements and immunoprecipitation of culture media of [ 3 5 S]methionine-labelled mesangial cells. PDGF-BB dose-dependently suppressed the IL-1β- and forskolin-induced elevation of PLA 2 mRNA, as well as PLA 2 synthesis and secretion. In contrast, PDGF-AA had no inhibitory effect. The tyrosine kinase inhibitor genistein dose-dependently antagonized the inhibitory effect of PDGF-BB on IL-1β-stimulated PLA 2 secretion, thus suggesting that tyrosine phosphorylation may be required for PDGF-BB inhibition of PLA 2 gene expression in mesangial cells.