The interacting effects of potassium with the dopaminergic control of mineralocorticoid release were evaluated in normal man. Sixteen male healthy volunteers [27 ± 6 (s.d.) years] on a 200 mmol sodium (Na+) and 60 mmol potassium (K+) diet (control) received a K+load of 200 mmol/day for 6 days (high-K+diet). Basal plasma aldosterone and 18-OH-corticosterone (18-OH-B) levels were significantly increased after 6 days of the high-K+diet, whereas basal levels of 18-OH-deoxycorticosterone (18-OH-DOC) and corticosterone remained unchanged. Fifteen minutes after 10 mg i.v. of the dopaminergic antagonist, metocloprarnide, a significant increase was only obtained for basal plasma aldosterone and 18-OH-B levels. The absolute rise of aldosterone and 18-OH-B induced by metoclopramide was greater (P < 0.01) after K+supplementation. However, the relative increase of these hormones was similar before and after K+loading. Basal plasma renin activity increased significantly under high-K+diet.The results indicate that K+homeostasis must be taken into account when estimating absolute response of aldosterone and 18-OH-B to dopaminergic antagonism.