This study investigates the effect of pertubation of the normal pituitary-adrenal axis on concentrations of adrenocorticotropin (ACTH)-like immunoactivity in peripheral tissues. We used a polyclonal antibody (West antibody) to measure ACTH-like immunoactivity in glacial acetic acid extracts of five tissues in adult male rats at increasing times (1, 7, 14, and 28 days) after hypophysectomy or adrenalectomy, and in normal control rats.Concentrations of ACTH-like immunoactivity were similar to those previously reported in liver, colon, heart, and small intestine and were not significantly affected by either hypophysectomy or adrenalectomy. While hypophysectomy also had no effect in the kidney, adrenalectomy resulted in a four-fold increase in extractable immunoactivity, first noticeable at seven days (p<0.005), but increasing progressively to 28 days (p<0.0005). Gel filtration showed that most of the increase in activity in kidneys of adrenalectomized rats corresponded to the 4.5 kD form comprising most of the serum ACTH immunoactivity and suggesting that the activity increase in kidney was largely due to ACTH derived from blood.