BACKGROUND: Migraine triggered by oral contraception (OC)-free interval is very common and may be extremely severe, long-lasting and poorly responsive to analgesics (status migrainosus). The serotoninergic (5-HT) system is crucially involved in pain threshold and it is sensitive to estradiol (E-2). Therefore, we aimed to assess neuroendocrine correlates of OC status migrainosus in response to the direct central 5-HT agonist meta-chlorophenylpiperazine (m-CPP) and to test the effect of transdermal E-2 supplementation of the OC-free interval. METHODS: Clinical investigative protocol, single-blinded placebo-controlled treatment. Oral m-CPP (0.5 mg/kg body weight) challenge test was performed in 10 patients with status migrainosus occurring within 48 h of the discontinuation of a monophasic pill (30 mu g of ethinyl estradiol and 150 mu g of desogestrel) and in six healthy women assuming the same OC as controls. In a consecutive menstrual cycle, patients with OC status migrainosus underwent to the same test after they were blindly treated with 2.0 g of percutaneous E-2 gel or placebo daily during the pill-free interval. Plasma prolactin and cortisol levels and clinical characteristics of migraine attacks were evaluated. RESULTS: Women with OC-status migrainosus showed a derangement of prolactin release (F = 4.8; P < 0.01) and a lack of cortisol response (F = 5.8; P < 0.001) after m-CPP in comparison with controls. Transdermal E-2 during the pill-free interval significantly restored prolactin (F = 2.8; P < 0.01) and cortisol responses (F = 18.9; P < 0.001) against placebo and positively affected the duration (P < 0.001), the number of hours in which pain intensity prohibits daily activity (P < 0.001), the episodes of vomiting (P < 0.001) and the consumption of analgesics (P < 0.001). CONCLUSIONS: Status migrainosus triggered by OC-free interval is associated with impaired prolactin and cortisol responses following m-CPP challenge. Transdermal E-2 supplementation is able to restore neuroendocrine response to this specific 5-HT agent, exerting a positive clinical effect on the course of menstrually related migraine.