Homologous blood transfusion may increase generalized inflammation by stimulating a patient's immune system during an open heart operation using cardiopulmonary bypass (CPB). We examined the beneficial effects on lung function of having no homologous blood transfusion during pediatric open heart operations. Thirty-three consecutive patients with ventricular septal defect were divided into (a) an autologous blood transfusion (AB) group (n=16) consisting of patients in whom predonation of autologous blood was undertaken and so homologous blood was not transfused, and (b) a control group (n=17) consisting of patients in whom homologous blood was used with a leukocyte removal filter during and after operation. Patients' age, sex, body weight, and contents of primed solution of the bypass circuit were similar in the 2 groups. Arterial blood gas analysis was carried out several times and the respiratory index (RI) calculated. Postoperative duration of intubation, white blood cell counts, and CRP titer were also compared. RI immediately after CPB did not differ between the AB and control groups, but RIs 3 and 6h after operation were significantly lower in the AB than in the control group (0.43±0.08 vs. 0.79±0.15 and 0.38±0.07 vs. 1.60±0.17). Duration of intubation, white blood cell counts, CRP titer were not statistically different. The results suggest that avoiding transfusion of whole homologous blood elements works effectively for preventing lung dysfunction after CPB.