During two decades of migraine provocation studies with naturally occurring signalling molecules, vasodilators such as prostaglandin E(2), prostaglandin I(2) (prostacyclin) and prostaglandin D(2) were shown to be able to induce headache in man. To elucidate the role of inflammation and vasodilatation in the generation of headache, we investigated whether the pro-inflammatory and vasoconstricting prostanoid prostaglandin F(2a) (PGF(2a)) would cause headache in a human model of headache.