The hemodynamic and renal effects of mechanical ventilation with positive end-expiratory pressure (PEEP) were studied with and without continuous dopamine administration in ten patients who had acute pulmonary failure. The application of 20 cm H2O PEEP during mechanical ventilation resulted in improvements in arterial blood oxygen tension, from 63 +/- 6 to 81 +/- 12 torr (mean +/- SE), and intrapulmonary shunt fraction, from 29 +/- 3 to 21 +/- 3 per cent, whereas cardiac output, systemic oxygen transport and renal function were impaired by 20, 19 and 47 per cent, respectively. Dopamine infusion at a rate of 5 +/- 0.05 micrograms/kg/min reversed the deleterious effects of PEEP on cardiovascular and renal function: cardiac output increased from 4.5 +/- 0.3 to 6.0 +/- 0.51, urinary output from 1.0 +/- 0.3 to 1.7 +/- 0.4 ml/min, sodium excretion and creatinine clearance by 50 per cent. Systemic oxygen transport was improved from 680 +/- 44 to 925 +/- ml, arterial oxygen tension from 81 +/- 12 to 102 +/- 14 torr, and total deadspace to tidal volume ratio from 0.49 +/- 0.02 to 0.44 +/- 0.03 with dopamine. The authors conclude that the depression of cardiovascular and renal functions that may occur in patients who need high levels of PEEP for the treatment of acute pulmonary failure can be treated successfully with dopamine infusion. This represents a valuable alternative to expansion of blood volume for the improvement of systemic oxygen transport and arterial blood oxygen tension in critically ill patients.