HANEW, K., SUGAWARA, A., UTSUMI, A., SHIMIZU, Y. and YOSHINAGA, K. GHRH and TRH Tests in Patients with Idiopathic and Secondary GH Deficiency -With Special Reference to GH Response Patterns to GHRH. Tohoku J. Exp. Med., 1990, 160 (3), 189-202-To study whether patients with idiopathic GH deficiency (IGHD) show a delayed GH response pattern to GHRH, 42 patients with IGHD, 14 patients with hypothalamic tumor (2ry GHD), and 23 normal short children (NSC) were examined as to their GH response patterns to GHRH together with their TSH and PRL response patterns to TRH. After TRH injection, the mean time of the TSH peak in IGHD (67.5±6.5min, n=36) and 2ry GHD patients (81.7±14.8min, n=9) was clearly delayed comparing to that of NSC (29.1±2.9 min, n=16; both p<0.01). Similarly, the mean time of the PRL peak in IGHD (38.3±3.6min, n=36) and try GHD patients (39.5±5.8, n=11) was significantly delayed comparing to NSC (22.0±3.5min, both p<0.01). In IGHD patients, the delayed response pattern of TSH and PRL was more remarkable in patients who had breech delivery than in those with normal delivery. In contrast, the mean time of the GH peak was similar in IGHD (62.1±4.0min, n=41), try GHD (64.1±8.1min, n=11) and NSC (58.0±6.1min, n=23). However, the decline from peak GH (120min GH/peak GH) was significantly smaller in IGHD (54.3± 4.2%) and try GHD (60.7±7.3%) than in NSC (39.0±8.1%)(both p<0.05). Further, in IGHD patients plasma GH response was greater in patients with normal delivery than in those with breech and asphyxia delivery. These results seem to indicate: 1) the stimulus-secretion mechanism is different between somatotrophs and thyrotrophs or lactotrophs in man, 2) IGHD patients have hypothalamic lesions as well as pituitary lesions, 3) such hypothalamo-pituitary lesions in IGHD patients are greater in patients with abnormal delivery than in those with normal delivery.