BACKGROUND: Although modified Mapleson D systems connected to ventilators have been used for controlled ventilation of anesthetized infants and children, the complexity of factors affecting rebreathing within the Mapleson D circuit has resulted in a variety of recommendations for fresh gas flow and minute ventilation. We constructed a formula for ventilator settings which would provide normal tidal volume, respiratory rate, and minute ventilation without rebreathing during mechanical ventilation in pediatric anesthesia and would like to compare this method to commonly recommended Bain-Spoerel's method. METHODS: Seventy eight infants and small children who anesthetized with enflurane and nitrous oxide were studied. We performed controlled ventilation with each method and measured SpO2, PETCO2 at 10, 20, 30 min after anesthetic induction. At 20 min after anesthetic induction, we drew a arterial blood sample to evaluate PaCO2 and PaO2. RESULTS: In patients above 10 kg, mean PaCO2 was within normal range. But in patients below 10 kg, PaCO2 was significantly higher(p<0.01) with the Bain-Spoerel's method than with the Paik Hosp.'s method. CONCLUSIONS: We conclude that our method for ventilator settings can be safely and competently applied to mechanical ventilation with Modified Mapleson D circuit in pediatric anesthesia.