These studies examine the effect of sodium (Na) and potassium (K) intake on the pressor and metabolic actions of ACTH (20 μg/kg/day) in sheep. After 21 days on each of five regimens in which Na and K intake varied from 0 to 100 mmol/day, no simple relationship between Na and K intake and blood pressure was found. After five days of ACTH treatment, mean arterial pressure (MAP) rose + 5 mmHg in sheep on 0 mmol Na, 0 mmol K (expressed as 0Na0K); + 13 mmHg on 10Na700K; + 5 mmHg on 0Na700K; + 20 mmHg on 700Na0Kand + 24 mmHg on 700Na700K.Plasma [K] was unchanged by ACTH on 0Na0Kbut fell in sheep on the other electrolyte regimens. Water intake increased with ACTH on all regimens except 700Na0K. Blood aldosterone concentration was high in sheep maintained on 0Naregimens but lower after five days of ACTH treatment in all groups. Blood cortisol and corticosterone concentrations increased with ACTH on all regimens studied.