In these experiments, Pitressin and oxytocin were investigated as substances that might possibly act to release TSH from the pituitary gland in a manner analogous to the corticotrophin releasing factor. Thyrotrophin release was inferred from in vivo measurements of thyroid I131 release rate in three types of rat preparations: 1) normal animals, 2) adrenalectomized rats maintained on 0.9% sodium chloride in the drinking water and cortisone 2.5 mg./day, 3) rats with lesions in the "thyrotrophic" area of the hypothalamus. Drugs were given sub-cutaneously in 25% polyvinylpyrrolidone solution. It was found that Pitressin in dosage up to 500 mU. every 8 hours and oxytocin in dosage of 233 mU. every 8 hours failed to influence thyroid activity.