To determine the role of known secretagogues in the aldosterone response to dopamine blocking agents, plasma levels of ACTH, angiotensin II, potassium and plasma catecholamines were measured in five normal male subjects before and after intravenous injection of saline or 10 mg metoclopramide. There were no consistent changes in hormone levels after saline injection. After metoclopramide, plasma aldosterone increased three-fold to peak values at 20 min post-injection. A significant increase in aldosterone was observed within 10 min during which period there was no significant change in plasma ACTH, plasma renin activity AII or K. Plasma levels of cortisol, noradrenaline, adrenaline and dopamine showed no significant changes after injection of metoclopramide which induced a ten-fold rise in plasma prolactin. These results provide direct evidence that factors other than the plasma concentration of ACTH, AII and K--or fluctuations in plasma catecholamines--are likely to be responsible for the acute increase in plasma aldosterone after metoclopramide injection in normal man.