Prolonged coma afterhead trauma is associated with depletion of 3', 5' cyclic adenosine monophosphate (cAMP) in the cerebrospinal fluid (CSF). Because cAMP has previously been implicated in neurorendocrine secretion, this study examines the pituitay-hypothalamic function in 15 adult male patients (to exclude the effects of puberty and menses) with traumatic coma lasting longer than 2 weeks. Ventricular CSF cAMP was measured at 2- to 4-day intervals for 10 to 25 days. Simultaneously, plasma hormone concentrations were also determined. In all 15 cases, CSF cAMP and plasma levels of thyroid-stimulating hormone (TSH), thyroxine (T4), free T4, triiodothyronine (T3), luteinzing hormone (LH), follicle-stimulating hormone (FSH), and testerone became subnormal. In 11 patients whose level of consciousness fluctuated, the reduction in plasma T4 and testerone were proportional to both severity of coma ( r greater than 0.81, p less than 0.05) and depletion of CSF cAMP (r greater than 0.81, p less than 0.05). In four patients who remained deeply comatose for 17 to 25 days, the hypothyroidism and hypogonadism persisted. In six patients who regained consciousness, both endocrine defects improved partially or completely. Injection of 1) thyrotrophic-releasing hormone and 2) gonadotrophic-releasing hormone elicited normal or supernormal increases in plasma concentrations of 1) TSH, and 2) LH and FSH, reduced, respectively, suggesting a suprahypophyseal deficiency. These observations demonstrate that suprahypophyseal hypothryoidism and hypogonadism may occur regularly in patients with traumatic coma lasting longer than 2 weeks.