Background: Intravenous infusion of pituitary adenylate cyclase-activating polypeptide-38 (PACAP38) provokes migraine attacks in 65-70% of migraine without aura (MO) patients. We investigated whether PACAP38 infusion causes changes in the endogenous production of PACAP38, vasoactive intestinal polypeptide (VIP), calcitonin gene-related peptide (CGRP), tumour necrosis factor alpha (TNF alpha), S100 calcium binding protein B (S100B), neuron-specific enolase and pituitary hormones in migraine patients. Methods: We allocated 32 previously genotyped MO patients to receive intravenous infusion PACAP38 (10 pmol/kg/minute) for 20 minutes and recorded migraine-like attacks. Sixteen of the patients were carriers of the risk allele rs2274316 (MEF2D), which confers increased risk of MO and may regulate PACAP38 expression, and 16 were non-carriers. We collected blood samples at baseline and 20, 30, 40, 60 and 90 minutes after the start of the infusion. A control group of six healthy volunteers received intravenous saline. Results: PACAP38 infusion caused significant changes in plasma concentrations of VIP (p = 0.026), prolactin (p = 0.011), S100B (p0.05). There was no difference in the changes of biochemical variables between patients with and without the MEF2D-associated gene variant (p>0.05). Conclusion: PACAP38 infusion elevated the plasma levels of VIP, prolactin, S100B and TSH, but not CGRP and TNF alpha. Development of delayed migraine-like attacks or the presence of the MEF2D gene variant was not associated with preictal changes in plasma levels of neuropeptides, TNF alpha and pituitary hormones.