We report the use of prostaglandin I.2. (PGI2) in three small children weighing less than 15 kg at high risk of graft thrombosis after cadaveric renal transplantation complicated by acute tubular necrosis. PGI2 was started at a dose of 5 ng/kg per min within the first 6 h after transplantation, and was continued for 12-15 days. Before and during PGI2 infusion, color-coded and pulsed Doppler sonography was performed. We found immediate restoration of diastolic flow, consistent with a decrease in vascular resistance. During the subsequent days, the sonographically assessed flow pattern and clinical graft function improved gradually. None of the three consecutively treated children developed graft thrombosis or lost his graft; no clinically relevant bleeding or adverse hemodynamic or pulmonary effects were seen.