The effect in isolated rat aorta of propofol, thiopentone, midazolam, etomidate and fentanyl on the impairment of endothelium-dependent relaxation by reactive oxygen species is reported. Aortic rings were exposed to reactive oxygen species by the electrolysis of the bathing physiological buffer, and endothelium dependent relaxation in response to acetylcholine was inhibited. This inhibition was countered by incubation before electrolysis with propofol (2 × 10−5 and 6 × 10−5M) or thiopentone (10−5 − 10−5M), but not with midazolam (3 × 10−4M), etomidate (3 × 10−4M) or fentanyl (3 × 10−5M). We suggest that the protective effect of propofol and thiopentone against the loss of endothelium-dependent relaxation caused by reactive oxygen species may be because of their antioxidant and free radical scavenging properties, which could be clinically relevant during surgical procedures in which ischaemia is unavoidable.