Vasopressin levels in plasma rise during migraine attacks. Vasopressin also induces endothelin-1 synthesis in endothelial cells, suggesting a role as a mediator of elevated plasma endothelin-1 in migraine. To explore a possible relationship between endothelin-1 and vasopressin in migraine, plasma concentrations of both peptides were monitored simultaneously throughout an attack and during two migraine-free intervals (control) in 20 patients. Endothelin-1 was elevated 6 h after the onset of an attack (3.3 +/- 0.3 pg/ml vs 2.7 +/- 0.2 pg/ml during migraine-free intervals; p = 0.12) whereas vasopressin was increased over control levels (2.8 +/- 0.3 pg/ml) by 3 h (3.6 +/- 0.4 pg/ml; p < 0.05) and remained elevated at 6 h (3.9 +/- 0.5 pg/ml; p < 0.01). These data suggest that vasopressin may act as a peripheral mediator of increased plasma endothelin-1 in migraine.