BACKGROUND: During pediatric general anesthesia with Mapleson D-circuit, we used large amount of FGF(fresh gas flow) for avoidance of rebreathing of expired gas but low FGF are employed, the amount of anesthetic consumption and air contamination can be reduced. The aim of this study was to evaluate the fact that FGF of 220 ml/kg/min is clinically acceptable. METHODS: We selected sixty children weighing < or =20 kg who were scheduled for inguinal hernia repair under general anesthesia. The study was performed by 2 steps; In the step 1, the patients were divided into two groups according to weight(less than or greater than 8 kg) and end-tidal Pco2 were compared with simultaneous arterial Pco2 measurements. In the step 2, the patients were divided into two groups according to FGF(2MV or 220 ml/kg) and arterial Pco2, end tidal Pco2 and PminCO2(minimum inspired Pco2) were measured. RESULTS: In the step 1 study, arterial Pco2 was significantly higher than end-tidal Pco2 in the group 1 and there was slight difference in arterial Pco2 and end-tidal Pco2 in the group 2. In the step 2 study, PaCO2, PetCO2, PminCO2 were significantly increased in the group 3 than group 2 but there were no clinical hypoxemia in all patients. CONCLUSIONS: We consider that FGF of 220 ml/kg/min is appropriate during controlled ventilation with Mapleson D circuit in children weighing > or =8 kg because of economic and ecological advantages. Also, we consider FGF can be reduced in children weighing <8 kg under accurate respiratory gas monitoring.