Changes in dopaminergic tonus have been hypothesized in patients with common migraine, suggesting that prolactin may play a role in the pathogenesis of the migraine. We investigated the prolactin response to domperidone, a dopamine receptor blocker. We tested 22 patients with common migraine (8 men, 7 women in the follicular phase of the menstrual cycle, and 7 women in the luteal phase), and 22 normal subjects adjusted for age, sex and phase of the menstrual cycle. Domperidone produced a significant rise of serum prolactin (p less than 0.01) in migrainous patients (7.77 +/- 3.09 vs 71.06 +/- 9.97 in men, 7.05 +/- 2.3 vs 129.58 +/- 14.15 in women in the follicular phase of the menstrual cycle, and 14.28 +/- 3.51 vs 169.71 +/- 16.63 in women in the luteal phase) and control subjects. The response did not show significant differences between migrainous patients and normal subjects. These data do not suggest changes in the tuberoinfundibular dopaminergic tonus in migrainous patients, in contrast to reports of other authors.