The effect of neurokinin A on human temporal muscle blood flow was compared to saline when injected into the muscle in six normal subjects. The 133-Xenon washout technique was used and the test solutions administered in a double-blind, cross-over manner. Neurokinin A (0.02 ml, 10(-5)M) caused a blood flow increase of 193%, while saline caused an increase of 23%. The difference between neurokinin A and saline was significant (p less than 0.05). It is suggested that a possible pathophysiological role of neurokinin A in migraine must involve modulation of vascular response as well as of primary nociception.