In anesthetized rats, the contribution of calcitonin gene related peptide(CGRP) to antidromic vasodilation of skeletal muscle blood flow(MBF) and nerve blood flow(NBF) following electrical stimulation of afferents in the dorsal roots was investigated by measuring the biceps femoris MBF and sciatic NBF using laser Doppler flowmetry. Increases in MBF and NBF were observed following repetitive antidromic electrical stimulation of unmyelinated C fibers in the ipsilateral dorsal roots between the L3 and L5 segments and between the L3 and S1 segments, respectively, without significant changes in systemic arterial blood pressure. The increases occurred during and several minutes after the end of 10 30 s stimulation. The responses were totally abolished by topical application of hCGRP(8 37), a CGRP receptor antagonist. It is cooncluded that antidromic vasodilation in biceps femoris muscles and the sciatic nerve following stimulation of unmyelinated C afferents in the dorsal roots is independent of systemic blood pressure and is mediated essentially by CGRP. It is suggested that this CGRP related antidromic vasodilation may be important in the clinical improvement of skeletal MBF and NBF produced by physical therapy, e.g. acupuncture. In anesthetized rats, the contribution of calcitonin gene related peptide (CGRP) to antidromic vasodilation of skeletal muscle blood flow (MBF) and nerve blood flow (NBF) following electrical stimulation of afferents in the dorsal roots was investigated by measuring the biceps femoris MBF and sciatic NBF using laser Doppler flowmetry. Increases in MBF and NBF were observed following repetitive antidromic electrical stimulation of unmyelinated C fibers in the ipsilateral dorsal roots between the L3 and L5 segments and between the L3 and S1 segments, respectively, without significant changes in systemic arterial The pressure were totally abolished by topical application of hCGRP (8 37), a CGRP receptor antagonist. It is cooncluded that antidromic vasodilation in biceps femoris muscles and the sciatic nerve following stimulation of unmyelinated C afferents in the dorsal roots is indepe ndent of systemic blood pressure and is mediated essentially by CGRP. It is suggested that this CGRP related antidromic vasodilation may be important in the clinical improvement of skeletal MBF and NBF produced by physical therapy, e.g. acupuncture.