Ten patients in severe cardiac failure were treated with dopamine (4 microgram/kg . min) and dobutamine (7.5 microgram/kg.min). Both drugs brought about a similar increase in stroke volume and cardiac output of about 50% and 60%, respectively, accompanied by a fall in peripheral vascular resistance of about 33%. On dopamine the heart rate increased by 12%, but remained unaltered on dobutamine. There was a significant fall in the preload of both ventricles with dobutamine, while ventricular filling pressure during dopamine infusion was only slightly decreased, unchanged or even increased. The pulmonary (wedge) pressure during dopamine infusion averaged 9 mm Hg higher than during dobutamine (P less than 0.001). There is thus the potential danger with dopamine of aggravating pulmonary congestion. Furthermore, the improvement in cardiac function due to dopamine is at the expense of a higher oxygen demand than with dobutamine. Dobutamine is, therfore, preferable to dopamine in the treatment of advanced myocardial failure.