Out of 16 patients with active acromegaly, 6 increased plasma GHafter LRH and 10 after TRH administration. These increases were unrelated to basal plasma GH levels and to plasma GH responses to insulin and arginine. Two patients who responded to LRH did not increase plasma GH after TRH. is suggested that these GH responses to non-specific releasing hormones may be due either to an alteration of the cellular membrane or to an extra-pituitary action, probably at a hypothalamic locus, of these peptides.