SummaryTwelve patients presenting an acromegalic syndrome (six men and six women) were studied from the point of view of thyroid, adrenal and gonadal functions. Acromegaly with global hyperfunction has not been observed. A certain degree of hypercorticism was demonstrated in several female patients. On the other hand, eleven of these patients showed signs of hypofunctioning of one or more endocrine glands. Four of them, which had not been submitted to any particular treatment, were completely pituitary-deficient (Simmonds disease, burned-out acromegaly).The results of pituitary radiotherapy must then carefully been intrepreted in the light of a possible spontaneous, regressive evolution of the intrasellar tumor by thrombosis, hemorrhage, compression and necrosis.In some cases, a thorough history taking of the patient reveals an additional point of interest : that sometimes a primary target-gland insufficiency, especially gonadal, may precede by several years the eruption of the hypertrophic phenomenon caused by acromegaly. The hypothesis of an acromegaly secondary and reactional to a peripheral endocrine deficit is evoked.One male patient presenting signs of a fullblown hypofunction of the pituitary was submitted to a metabolic observation to study the effects on electrolytes excretion during ACTH injections and the oral administration of cortisone, hydrocortisone and prednisone. Prednisone appeared to be remarkably effective as substitution therapy.