A paediatric breathing system, called the Emona system has been devised because commercially available anaesthetic baby systems used in head and neck surgery did not give satisfactory results. The system provides for fresh gas inflow while the expiratory path is positioned close to the patient. A precise description and schematic presentation of its action is given. The efficiency of the Emona system was tested in 65 infants and children using blood gas analyses. Furthermore, CO2 analyses of mixed expired and inspired gases, as well as some measurements applying the respiratory nomogram, were carried out. The efficiency of the Emona system is compared with results of some other baby systems (Jackson-Rees and Ruben's systems). The problems of paediatric anaesthetic systems are discussed and the dilemma of normal values for some respiratory parameters in children exposed. The results show that the Emona system is particularly advantageous in manually controlled ventilation in comparison to the results of other authors applying mechanical respiratory support.