Background: Intravenous infusion of 10 pmol/kg/min pituitary adenylate cyclase-activating polypeptide-38 (PACAP38) induces migraine-like attacks in migraine patients without aura (MO). Here, we conducted a pilot study and investigated if lower doses of PACAP38 exert similar migraine-inducing abilities. Methods: We randomly allocated six MO patients to receive intravenous infusion of 4, 6, and 8 pmol/kg/min of PACAP38 over 20 minutes in a double-blind, three-way cross-over study. Headache and migraine characteristics were recorded during hospital (0-2 hours) and post-hospital (2-13 hours) phases. Results: PACAP38 induced migraine-like attacks in one out of six patients with 4 pmol, two out of six patients with 6 pmol and three out of six patients with 8 pmol (p = 0.368). All patients reported head pain after 8 pmol/kg/min, whereas five of six participants reported head pain after both 4 and 6 pmol/kg/min. We found no difference between the three doses in the AUC for headache intensity over the 12-hour observation period (p = 0.142). An exploratory analysis showed a significant difference between 4 pmol and 8 pmol (p = 0.031). Conclusion: A trend of a dose-response relationship between dose of PACAP38 and incidence of migraine was observed. We suggest that 10 pmol/kg/min PACAP38 is the most optimal dose to induce migraine-like attacks.