This study was undertaken to determine whether ketamine can exert any action on basal endothelium derived relaxing factor (s) release and vasodilator effect of acetylcholine on phenylephrine induced contractile responses in isolated rabbit aortic strips. Ketamine did not induce any contractile response in the aortic strips at various concentrations ( 1to 10'3 M). Ketamine did not significantly alter phenylephrine-induced contractions at lower concentrations (10'8 to 10‘5 M), but at higher concentrations (10‘4 to 10'3 M) the depression caused by ketamine was significant in both endothelium intact and denuded strips. Propranolol, methysergide, atropine, diphenhydramine and indomethacine did not block the relaxant effect of ketamine. Pretreatment of the endothelium intact strips with ketamine (10'5 M) had no effect on the relaxant effect of acetylcholine which was observed on endothelium intact aortic strips. The relaxant effect of ketamine on the isolated rabbit aortic strips does not seem to interact with the changes in the release of EDRF from endothelial cells.