This study was designed to investigate vasopressin receptor status (Bmax and Kd) on platelets, vasopressin plasma levels, and vasopressin-induced platelet aggregation in migraine patients (21 females and 6 males) during a headache-free interval and in a matched control group. In the migraine group, Bmax was significantly higher (P = 0.02) at 53.9 +/- 20.6 fmol/mg than in the control group (36.8 +/- 21.0 fmol/mg). A correlation between Bmax and high or low sensitivity to vasopressin as an aggregator was evident in the control group, but not in the migraine group. No differences in Kd or in plasma levels of vasopressin between the migraine and control group were apparent. Men in both groups were much less sensitive to vasopressin as a platelet aggregator than were women (P < 0.01). Whether the higher Bmax in the migraine group is a reflection of temporarily higher vasopressin levels during headache or reflects a primary increase in sensitivity to vasopressin, remains to be clarified. The higher sensitivity of platelets (as a model for vessel wall receptors) from women may indicate why many more women than men suffer from migraine. Since the Bmax of the vasopressin receptor on platelets from migraine patients is increased compared to controls, treating migraine headache with vasopressin may deserve more attention.