The aim of this study is to demonstrate how easy and suitable is the closed system in infants and children. An original circuit, adapted from the Bain-Spoerel system, is used. Its principle is to draw-up the expired gas through a soda lime canister by a pump, whose flow is 14 l.min-1. ("Circuit Bisontin"). For this study, 20 infants and children underwent anesthesia with isoflurane, in spontaneous or mechanical ventilation (with a "bag in the bag" principle ventilator). The lowest body weight was 2.7 kg. The advantages are a minimal dead space and no expenditure of energy during spontaneous ventilation thanks to an internal high flow and the absence of internal one-way valve. Gas monitoring is achieved by a four gas analyser (Capbomac Datex).