Metoclopramide is a dopamine receptor antagonist and, in large doses, has been shown to reverse the increase in renal blood flow, the diuresis and the natriuresis produced by a low-dose infusion of dopamine. We gave a single iv. dose of metoclopramide 10 mg to 21 patients on an intensive care unit who were haemodynamically stable and receiving dopamine 3 mug kg-1 min-1. Renal vascular resistance index, measured by duplex Doppler ultrasonography, did not, change after metoclopramide. Renal function, measured by creatinine and osmolar clearance, natriuresis, kaliuresis and excretion fractions of sodium and potassium did not change after metoclopramide. We conclude that normal doses of metoclopramide (< 0.2 mg kg-1) do not antagonize the renal effects of a low-dose infusion of dopamine in critically ill patients.