Prostacyclin [prostaglandin I(2) (PGI(2))] activates and sensitizes meningeal sensory afferents. In healthy subjects PGI(2) triggers headache in healthy subjects. However, the migraine-eliciting effect of PGI(2) has not been systematically studied in patients with migraine. We hypothesized that intravenous infusion of the stable prostacyclin analogue epoprostenol would trigger migraine-like attacks in migraineurs. We infused 10 ng kg(-1) min(-1) PGI(2) or placebo over 25 min in 12 migraineurs without aura in a controlled, double-blind, cross-over study and recorded headache intensity and associated symptoms, velocity in the middle cerebral artery (V(MCA)) and diameter in the superficial temporal artery. In the period 0-14 h, 12 subjects reported headache on PGI(2) day compared with three subjects on placebo day (P = 0.004), and six subjects fulfilled the criteria for an experimentally induced migraine-like attack compared with two subjects on placebo (P = 0.219). During infusion and post-infusion phases the AUC under the headache curve on PGI(2) was significantly larger than on placebo (P < 0.05). There was a significant V(MCA) decrease (P = 0.015) and superficial temporal artery diameter increase (P < 0.001) on PGI(2) compared with placebo. In conclusion, PGI(2) may trigger a migraine-like attack in migraine sufferers. We suggest sensitization of perivascular nociceptors and arterial dilation as the mode of action of PGI(2)-induced headache and migraine-like attacks.