Seven goitrogens were studied to determine whether adrenal atrophy was a characteristic response to administration of antithyroidal agents. Treatments consisted of administration of thiouracil (0.1%), Tapazole (Lilly, 0.001%, 0.005% and 0.01%) and potassium perchlorate (1%) in drinking water and feeding of low iodine diet, p-aminosalicylic acid (PAS, 1%, 2%, 4%), p-aminobenzoic acid (PABA, 2%, 4%) and sulfaguanidine (2%, 4%) in the diet. After 12 weeks of treatment, the animals were anesthetized with sodium pentobarbital, blood was withdrawn by cardiac puncture for steroid analyses and the weights of the pituitary, thyroid, adrenal and thymus glands were determined. Treatment with thiouracil, Tapazole, perchlorate, PABA and sulfaguanidine induced an atrophy of the adrenal gland. Administration of PAS and the low iodine diet brought about hypertrophy of the thyroid gland without adrenal atrophy. Feeding with PABA, at the level of 2% in the diet, induced adrenal atrophy without thyroid hypertrophy while at the 4% level both thyroid hypertrophy and adrenal atrophy occurred. PABA at both dose levels brought about a shift in plasm corticoid levels. Plasmaa from rats given PABA was found to contain little or no corticosterone while the concentration of 17-hydroxycorticoids was markedly increased.