In in vitro experiments, we showed that hydrogen sulfide used in concentrations from 10 -6 to 10 -3 M caused dose-dependent relaxation of circular preparations of the aorta and mesenterial and renal arteries. With increase in the H 2 S concentration to 10 -2 M, we observed intensification of the relaxing effect only with respect to preparations of mesenterial and renal arteries. Vasorelaxation of walls of the aorta and mesenterial and renal arteries induced by applications of cysteine (10 -6 to 10 -2 М) was completely inhibited in the presence of propargylglycine. Homocysteine used in relatively high concentrations (10 -4 to 10 -2 М) caused a decrease in the endothelium-dependent vasorelaxation induced by acetylcholine. The renal and mesenterial arteries demonstrated the maximum sensitivity to homocysteine, while the minimum sensitivity was demonstrated by the aorta. Pre-incubation of the vessels together with L-NAME and indomethacin decreased the vasorelaxing action of hydrogen sulfide, while pre-incubation of the studied vessels with sodium nitroprusside intensified such action.