The aim of this study was to compare the efficacy of two inotropic infusions in treating low BP in preterm neonates. Forty infants with median gestational age 27 weeks (range 23-33) were studied. At trial entry the infants, who all had a systolic BP < 40 mmHg despite receiving a colloid infusion, were randomized to receive either a dopamine or dobutamine infusion. The infusions were commenced at a rate of 5 micrograms/kg per min and, if necessary, this was increased over the 3 h study period to 15 micrograms/kg per min. There was no significant difference in the gestational or postnatal age or baseline BP of the 20 infants who received dopamine and those 20 who received dobutamine. Three hours after commencing the infusions, although there was no difference in the rate of inotrope infusion between the two groups, the infants who received dopamine had a significantly higher systolic BP, a median of 39 mmHg (range 30-58) compared to a median of 34 mmHg (range 21-46) in the dobutamine group, P < 0.05. In addition, 10 infants who received dopamine, but only 3 who received dobutamine, had a systolic BP > 40 mmHg (P < 0.05). We conclude that dopamine rather than dobutamine infusion is more efficacious in improving the BP of preterm neonates.