BACKGROUND: The purpose of this study was to evaluate the safety and efficacy of low-flow anesthesia with a semi-closed circle anesthesia system in infants. METHODS: Twenty, ASA physical status 1 or 2, infants were randomly assigned into two groups: high-flow anesthesia (HFA) or low-flow anesthesia (LFA). An identical semi-closed Dr ger circle anesthesia system (Cato) was used to all patients. Initial fresh gas flow (FGF) was N2O 1.5 L/min and O2 1.5 L/min in both groups. This FGF of 3 L/min was maintained in the HFA group. After 10 min of HFA, the FGF was reduced to 500 ml/min (N2O 250 ml/min and O2 250 ml/min) in the LFA group. RESULTS: Hypoxic or hypercarbic gas concentrations were not observed in all patients. Enflurane consumption during LFA was about 1/3 of that during HFA (6.8 +/- 1.3 ml vs. 19.5 +/- 5.8 ml). The mean highest esophageal temperature was similar in both groups. The mean highest inspiratory gas and soda lime temperatures were significantly higher in the LFA group than in the HFA group. CONCLUSIONS: Low-flow anesthesia in a circle system with a fresh gas flow of N2O 250 ml/min and O2 250 ml/min could be performed safely and economically for infants.