Normal rat kidney fibroblasts, density-arrested in the presence of epidermal growth factor (EGF), can be restimulated to proliferate in a synchronous way and acquire a transformed phenotype following treatment with additional growth factors like retinoic acid (RA) and transforming growth factor (TGF)-beta. It was found that bradykinin has a strong inhibitory effect on growth stimulation induced by these factors, an effect which cannot be mimicked by PGF2 alpha. The growth-inhibiting effect can be blocked by inhibitors of cyclo-oxygenase activity, indicating that the relevant second messenger is most likely a prostaglandin. Externally added PGJ2, at a concentration of 10 microM, can mimic the inhibitory effect of bradykinin on the loss of density-arrest induced by RA suggesting that PGJ2 is a possible candidate for being the bradykinin induced growth-inhibiting prostaglandin.