Arteriovenous anastomoses (AVAs) may open up during migraine attacks. In studies with anaesthetized and bilaterally vagosympatectomized pigs, triptans reduce AVA blood flow and increase the arteriovenous O2 difference (AVDO2). To investigate whether subcutaneous sumatriptan 6 mg could induce changes in the AVDO2, we measured the AVDO2 in the external jugular vein in healthy subjects. We also measured the AVDO2 in the internal jugular and cubital veins. There were no changes in AVDO 2 after subcutaneous sumatriptan, probably because AVA blood flow is limited in humans with an intact sympathetic nervous system.