In order to determine the platelet characteristics responsible for aggregation, the number and apparent dissociation constant (K D aPP ) of fibrinogen receptors were determined in 12 women with common migraine. The studies were performed by the use of 125 -fibrinogen. The patients were assessed in headache-fee intervals. The mean number of platelet fibrinogen receptors exposed in migraine patients was significantly higher than those obtained in healthy controls (p<0.05). The (K D aPP ) in migraineurs was about three times lower than in the controls (p<0.02). The results indicate that both the number and affinity of fibrinogen receptors or platelets are increased in migraine patients. The authors conclude that this phenomenon may be responsible for the increased number of circulating platelet aggregates in migraine patients and for the prevalence of various kinds of strokes during migraine attacks.