Abstract STUDIES in this laboratory have shown that exposure of grouped chickens to prolonged periods of social interaction resulted in adrenal hypertrophy accompanied by decreased reproductive function and gonadal degeneration (Flickinger, 1961, 1963, 1965). These endocrine adaptations to an environmental stimulus were believed to result from alterations in the secretion of trophic hormones of the anterior pituitary. Hence, the investigation reported herein was undertaken to measure the effects of prolonged administration of ACTH on the gonads and adrenals of sexually mature chickens. MATERIALS AND METHODS Single Comb White Leghorn chickens, hatched from a highly inbred strain, were housed in individual cages (2 sq. ft./bird) following brooding. A commercial poultry ration and drinking water were supplied ab libitum and photoperiods were set at 15 hours per day. When the birds reached 26 weeks of age, they received daily intramuscular injections of gelatin-suspended ACTH 3 for a period of 14 days. Vehicle-injected 4 birds of …