In eight patients (six males and two females) hospitalized for prolonged coma (164-1320 days; five patients were in traumatic coma, two after cardiac arrest during surgery, and one after a venomous scorpion sting), diurnal variation of cortisol secretion, human (L) GH, PRL, TSH secretion as well as the release of the pituitary hormones after TRH and L-dopa stimulation were assessed. Serum T4 cortisol, hGH, hPRL, and hTSH levels were normal. The cortisol diurnal variation was preserved in six patients. In seven of eight patients, the hPRL and hTSH responses to TRH test were normal and in five patients, there was a rise of more than 150% in serum hGH concentrations. After L-dopa administration, five patients responded with a rise in hGH. In three patients, there was no response of hGH to TRH or L-dopa. Five patients responded with significant reduction in the serum hPRL concentration after L-dopa, and in three patients, no change was observed. It was concluded that patients with prolonged coma have variable hypothalamic pituitary function. They preserve the cortisol diurnal variation and the hypothalamic- pituitary-thyroid axis as well as PRL secretion; however, hGH secretion may respond abnormally to various stimuli.