Plasma prorenin and renin changes after a bolus injection of 25 U intravenous adrenocorticotrophic hormone (ACTH, synacthen) were studied in seven untreated uncomplicated essential hypertensives over a period of 24 h. Plasma prorenin did not change significantly during the study, whereas renin after 24 h was higher than at baseline (4.3 +/- 0.6 versus 2.3 +/- 0.9 ng angiotensin I (Ang I)/ml per h, P less than 0.01). We conclude that endogenous glucocorticoid stimulation induced by exogenous ACTH and ACTH itself seem to induce a secondary or tertiary rather than a primary effect on the human renin gene.