Several arguments suggest that dopamine (DA) plays a role in the physiopathology of migraine. Conjugated and unconjugated plasma and platelet DA, as well as platelet phenolsulfotransferase M activity (responsible for DA sulfatation) were measured in 30 control subjects, 27 common migraine patients between attacks and 9 migraineurs during an attack. No modification of any of the parameters tested was detected in attack-free periods. During the attack no change of conjugated DA was observed; in contrast, a significant decrease of unconjugated platelet DA and a significant and correlated increase of plasma unconjugated DA were demonstrated. This corresponds to a release of unconjugated DA by the very dense bodies in platelets of migraine patients during the attack.