In this paper, isolated rabbit arteries (renal artery, RA; femoral artery, FA; basilar artery, BA) were used to study the effect of hypoxia on vasodilation induced by substance P (SP) and calcitonin gene-related peptide (CGRP). The results showed that hypoxia caused a marked decrease of the arteries, response to SP (10(-7) mol/L) and CGRP (2.8 x 10(-9) mol/L). Repeated hypoxia even resulted in a complete disappearance of response. On the second hypoxia, CGRP (2.8 x 10(-9) mol/L) induced vasodilation on BA was vanished. On the third hypoxia, vasodilation induced by CGRP (2.8 x 10(-9) mol/L) on FA and that induced by SP (2 x 10(-7) mol/L) on BA were vanished, and CGRP (2.8 x 10(-9) mol/L) induced a lesser extent of vasodilation on RA. At the fourth time, SP (10(-7) mol/L) -induced vasodilation of FA disappeared, and that on RA was small. At the fifth time, the effect of SP (10(-7) mol/L) on RA was nearly vanished. It is concluded that the effect of hypoxia on CGRP-induced vasodilation is stronger than that on SP-induced vasodilation, and the effect is most pronounced on the BA.