A new semi-closed anaesthetic system for newborns and small infants was developed by slightly modifying the circle system used for adults. The fact that this new system was employed with satisfactory results in anaesthetizing more than 50 children under 20 kilogram bodyweight weakens the argument that semi-closed circuits should be avoided in small children on account of high expiratory resistance, possibility of increased dead space, inefficient CO2 absorption and unpredictable inspiratory oxygen concentration. The advantages and disadvantages of the new system are reviewed.