Effect of intravenous administration of beta-hypophyamine (pitressin) on free 17-hydroxycorti-costeroid concentrations in plasma was determined in 7 normal, young, human subjects by the method of Silber and Porter. Pitressin was infused over a 2-hour period in doses varying from 6.8 to 30.0 units. An increase of 15 g[mu]% in plasma 17-hydroxycorticosteroids occurred during the second hour of Pitressin infusion whereas a decrease of 7 [mu]g% occurred at this time when a control infusion of saline was given. Associated with the significant increase in plasma 17-hydroxycorticosteroids was a significant decrease in the circulating eosinophils.