Hypothalamic pituitary functions were studied in 25 patients before and 6 months after cranial irradiation with or without radiosensitizing chemotherapy for nasopharyngeal carcinoma. The estimated average total dose was 5,000 cGy to the hypothalamus and pituitary gland. The radiosensitizing chemotherapy used was endoxan, 4900 +/- 873 mg and/or methotrexate 113 +/- 30 mg. All patients had normal pituitary function before radiotherapy. Six months after radiotherapy, there was a significant increase in baseline serum thyrotropin (TSH) and follicle-stimulating hormone (FSH) levels. The TSH response to thyrotropin-releasing hormone (TRH) was significantly increased, suggesting primary hypothyroidism due to neck irradiation. The peak serum TSH response to TRH became delayed in 21 patients, suggesting a defect in TRH release. In male patients who did not receive radiosensitizing chemotherapy, the FSH response to luteotropic hormone-releasing hormone (LHRH) increased while the luteinizing hormone (LH) response decreased. But in male patients who also received radiosensitizing chemotherapy, both the FSH and LH responses to LHRH increased. The adrenocorticotropic hormone (ACTH) response to ovine corticotropin-releasing hormone (CRH) did not change, while the integrated cortisol response increased. The growth hormone (GH) response to growth hormone-releasing hormone (GRH) did not change. The GH response to insulin tolerance test (ITT) increased and may be explained by the more severe hypoglycemia induced by the same dosage of insulin after radiotherapy or the recovery from the previous wasting caused by radiotherapy. There was no significant increase in serum prolactin. In conclusion, we demonstrated impairment of the hypothalamus-pituitary-endocrine gland axes as early as 6 months after cranial irradiation with or without chemotherapy.