Two groups of 15 children aged from 15 days to 6 years, undergoing surgery on cardiopulmonary by-pass for congenital heart disease have been retrospectively analyzed. Group A received a low-dose aprotinin treatment (30,000 KIU/kg in the priming solution); group C (control group) did not receive any aprotinin. Groups were homogeneous for pathology, cardiopulmonary by-pass time, aortic cross-clamping time, cyanotic/acyanotic patients ratio, temperature during cardiopulmonary bypass. A number of postoperative data were measured: activated clotting time was without any difference between aprotinin-treated and control patients; the same went for temperatures, urine output, intubation time, stay in Intensive Care Unit, coagulation tests, platelet counts, hematocrit, survival rate, and blood loss. Serum creatinine levels were significantly higher in group A than in group C both at the arrival in Intensive Care Unit (0.81 +/- 0.27 vs 0.66 +/- 0.12, p = 0.032) and in the first postoperative day (1.01 +/- 0.5 vs 0.72 +/- 0.19, p = 0.038). BUN was significantly higher in group A vs group C in the first postoperative day (43.6 +/- 21.1 vs 33.9 +/- 16.7, p = 0.043). We conclude that low-dose aprotinin did not reduce postoperative bleeding; we cannot exclude that higher dosages could be more effective, but the evidence of a moderate tubular function impairment suggests caution in using high-dose aprotinin in children.