This report deals with the influence of cortisone, prednisolone, prednisone and 9 α-fluorocortisol acetate on the serum antitryptic activity of normal, splenectomized, adrenalectomized and adrenalectomized-splenectomized rats. Elevation of serum antitryptic activity was most consistent with 9α-fluorocortisol acetate administration. Prednisolone and prednisone proved less effective while cortisone-induced changes were of small magnitude.