SUMMARYA double T-piece paediatric system is described. During spontaneous respiration, the system will perform like a Magill system if the fresh gas flow is delivered via the distal T-piece; the proximal T-piece will provide an outlet. During controlled ventilation the set will perform like a Rees system if the fresh gas flow is delivered via the proximal T-piece; the distal T-piece will provide a control outlet. As judged by the degree of rebreathing, distal inflow is more efficient than proximal inflow during spontaneous respiration. Distal and proximal inflow are equally efficient during controlled hyper-ventilation.