Adrenocorticotrophic hormone (ACTH) administration to sheep (100 IU/day) produces a sustained increase in arterial pressure within 24 h. The effect of ACTH on excretion of an intravenous saline load was tested in 8 adult cross-bred Merino ewes. A significant diuretic response to saline loading was found after 24 h but no increased natriuresis. On days 3 and 6, diuretic and natriuretic responses were both significantly increased. Steroid-induced sodium retention may have abolished the natriuretic effect on day 1.