1. Five normal subjects were studied under metabolic conditions on a controlled sodium and potassium intake.
2. Plasma and urine free dopamine concentrations were measured in these subjects before, during and after 5 days administration of fludrocortisone (0·2 mg twice daily).
3. Urine free dopamine showed a tendency to fall during the early phase of fludrocortisone administration and then rose towards normal.
4. In a patient with primary hyperaldosteronism there was no evidence of increased renal production of dopamine. Urine dopamine fell when plasma renin activity rose as a result of spironolactone administration (200 mg three times a day for 5 days).
5. If renal dopamine has a role in mineralocorticoid ‘escape’ then it may be permissive only. The mechanisms of control of dopamine production could include tubular sodium concentration, tubular chloride concentration and intrarenal renin activity.