Plasma levels of beta-endorphin and ACTH were measured during and outside migraine attacks in 17 patients with common migraine and 11 patients with classic migraine. Specific radioimmunoassays for beta-endorphin and ACTH were used. The beta-endorphin assay did not cross-react with beta-lipotropin. In common migraine, median plasma beta-endorphin was 3.3 pmol/l (95% confidence limits: 2.5-4.0 pmol/l) during attacks and 2.9 (2.4-3.2) pmol/l in the headache-free period. In classic migraine, plasma beta-endorphin was 3.2 (1.4-4.3) pmol/l during attacks and 2.4 (1.1-3.6) pmol/l outside attacks. ACTH plasma levels were 15 (10.5-20) pmol/l during and 15.7 (13.4-17) pmol/l outside attacks in common migraine. In classic migraine, plasma ACTH was 16 (7-36) pmol/l and 12.3 (8-28) pmol/l respectively. No significant differences were found between attacks and headache-free periods in common or classic migraine. Accordingly, we could not add evidence to the theory of a dysfunction of the endogenous opioid system in migraine.