To study the hormonal effects on hematologic parameters as indicators of chronic stress, exogenous adrenocorticotropin (ACTH) at 6.3 or 20.0 IU/kg/day and hydrocortisone at .25 or 2.5 mg/kg/day were administered parenterally to laying hens. Both ACTH treatments induced significant (P less than .05) heterophilia, monocytosis, eosinophilia, and basophilia. Significantly elevated leucocyte counts and lymphopenia (P less than .05) were observed with the high dosage of ACTH. Both hydrocortisone-treated groups developed an absolute lymphopenia and heterophilia (P less than .05). The low dosage of hydrocortisone induced a significant (P less than .05) monocytosis; the high dosage caused significant (P less than .05) decreases in the total eosinophil and basophil counts as well as an increase in the ratio of heterophils to lymphocytes. The hemopoietic parameters, especially heterophil counts, were sensitive indicators of a hormonal stress response induced by the administration of ACTH and hydrocortisone.