In this paper we examine the effect of the vasodilator peptide bradykinin on endothelial cell regulation of phosphoinositide (PI) turnover. The data show that the activation of PI turnover by bradykinin in bovine pulmonary artery endothelial cells is insensitive to pertussis toxin, which ADP ribosylates a membrane protein of mol wt 40,000. However, this effect of bradykinin can be potentiated by guanosine 5‘‐O‐(3‐thio)triphosphate (GTPγS), an activator of G proteins, and depressed by guanosine 5‘‐O‐(2‐thio)diphosphate (GDPβS), an inhibitor of G proteins. After endothelial cells were pre‐incubated for 1 h with GTPγS, there was a three‐ to fourfold increase in PI turnover. Preincubation of cells with GDPβS did not affect the basal level of PI turnover, but completely prevented activation of PI turnover by bradykinin. 4β‐Phorbol‐12β‐myristate‐13α‐acetate can block the bradykinin‐stimulated inositol monophosphate formation in cultured endothelial cells. The effects of bradykinin on PI turnover were blocked by B2antagonists but not by B1antagonists. Taken together, these results indicate that in endothelial cells the bradykinin B2receptor is coupled to phospholipase C via a G protein (or proteins) that is not a substrate for pertussis toxin (neither Ginor Go).— Voyno‐Yasenetskaya, T. A.; Tkachuk, V. A.; Cheknyova, E. G.; Panchenko, M. P.; Grigorian, G. Y.; Vavrek, R. J.; Stewart, J. M.; Ryan, U. S. Guanine nucleotide‐dependent, pertussis toxin‐insensitive regulation of phosphoinositide turnover by bradykinin in bovine pulmonary artery endothelial cells.FASEB J.3: 44‐51; 1989.