The effects of propofol and thiopental on three vasoconstrictors, acetylcholine, histamine, and serotonin were studied in isolated porcine and human coronary artery rings. Propofol and thiopental attenuated the contractile response to all mediators in a dose-dependent manner. This dilating effect was fairly weak using low concentrations (propofol 1 μg mL−1 and 10 μg mL−1, thiopental 5 μg mL−1 and 10 μg mL−1). In the presence of high concentrations (propofol 100 μg mL−1, thiopental 50 μg mL−1) marked relaxation was observed (propofol −32% up to −49%, P < 0,05; thiopental −23% up to −67%, P < 0.05). These dilating effects were seen both in intact and denuded rings, the differences were not significant. Human coronary artery segments were relaxed by thiopental (−22% to −76%) and propofol (−11% to −67%) to a similar extent. Our data indicate that propofol and thiopental relax isolated coronary segments in a dose-dependent manner, and that there is no evidence that these effects are dependent of endothelial factors.