Nineteen children, aged 2-54 months, requiring high-dose inotropic support after cardiac surgery, were given either dopamine or dobutamine in a blinded, double crossover, study. Using a pulmonary artery thermistor, right and left atrial cannulae, and pulmonary and femoral arterial catheters, conventional haemodynamic variables were measured hourly over three consecutive 4 h dopamine-dobutamine-dopamine or dobutamine-dopamine-dobutamine exchanges. No significant differences in haemodynamics occurred during dopamine therapy compared with the same dose of dobutamine in 14 patients receiving phenoxybenzamine 2 mg kg-1, four of whom had also received enoximone. In five patients, neither enoximone nor phenoxybenzamine was used and significant increases in pulmonary artery pressure and pulmonary vascular resistance (P = 0.04) occurred when patients were given dopamine rather than dobutamine. We conclude that dobutamine and dopamine are equipotent inotropes in children and that dopamine in doses > 7 micrograms kg-1 min-1, caused pulmonary vasoconstriction, an effect mediated by alpha adrenergic receptors.