Twenty chronic post-traumatic headache subjects (16 men and 4 women) were considered, together with age and sex matched normal controls. Pituitary function was challenged by means of luteinising hormone releasing hormone (100 mg,iv), thyrotropin (TSH) releasing hormone (200 mg,iv) and regular insulin (.1 U/kg,iv). The responses of gonadotropins, TSH, somatotropin (STH) and prolactin (PRL) were studied in the group as a whole and in clinical subgroups. No differences were found in the baseline levels of the hormones. No significant changes were observed in the responses of gonadotropins and STH. A decreased response was found for TSH and, in the female series, an enhanced response of PRL was observed. Patients complaining for a decreased libido showed a larger PRL response. The smaller response of TSH exhibits a straight inverse relationship to the clinical severity. The periodicity of PRL secretion studied in male patients with a harmonic analysis according to the Fourier's theorem showed the preservation of the physiological sleep-entrained night surge. The per cent incidence of the harmonics with a period shorter than 24 hours decreases according to the clinical severity, at variance to the finding in normal controls. The only persisting harmonic is the one with a 24 hour period. In the absence of major post-traumatic endocrine syndromes, post-traumatic headache subjects show changes of the neuroendocrine regulation of pituitary secretion. The findings are consistent with the hypothesis of an hyperactivity of serotoninergic neurotransmission.