A randomized double-blind study was carried out on 20 patients after coronary artery bypass surgery to investigate the effects of graded doses of dopexamine hydrochloride or placebo on systemic haemodynamic responses and renal vascular resistance index (RVRI) measured using Doppler ultrasound. Pre-operatively, all patients had good left ventricular function and normal renal function. Eleven were allocated randomly to receive incremental infusions of dopexamine 0.5, 1, 2, and 4 μg kg−1 for 40 min each, and nine received corresponding infusions of placebo. One patient was withdrawn from the dopexamine group because of tachycardia. In the remaining 19, heart rate (HR) and cardiac index (CI) were significantly (P < 0.05) increased from base-line with dopexamine: the HR values with dopexamine differed significantly from those with placebo at the 2 and 4 μg kg−1 min−1 dose, and at 4 μg kg−1 min−1 for CI. Systemic vascular resistance index (SVRI) fell significantly in both groups: the reduction was significantly greater with dopexamine 4 μg kg−1 min−1 than with the corresponding infusion of placebo. RVRI increased and urine output decreased significantly during the infusions in both groups, but with no significant difference between groups. There were no changes in systemic arterial pressures, pulmonary artery occlusion pressures, stroke volume index or left ventricular stroke work index. Where changes from base-line occurred in either group, they had not returned to base-line within 40 min of stopping the infusions (except perhaps for CI in the dopexamine group). Dopexamine appears to offer no particular protection to the renal vascular bed.