Eleven patients with severe head injuries were treated by artificial moderate hypothermia (32.0-33.0 degrees C). Measurement of the serum levels of anterior pituitary hormones (LH, FSH, TSH, and PRL) and the response of these hormones to the respective releasing hormones was done in the 11 patients before and during hypothermia. All 11 patients were under GCS 5. Those with brain death during hypothermia were excluded. Moderate hypothermia was performed for 3-7 days and involved cooling to 32.0-33.0 degrees C (Jugular venous blood temperature). The peak value of LH, FSH, TSH and PRL to administration of TRH or LH-RH during hypothermia were significantly lower than those before hypothermia, while basal values of those hormones were not affected by this treatment. These findings suggested that anterior pituitary function were suppressed by moderate hypothermia.