The following methods for monitoring the ventilation in general anaesthesia can theoretically be applied for neonates and small infants: The use of a precordial stethoscope, measurements and observation of the ventilation pressure, analysis of the inspiratory oxygen concentration, measurement of the expiratory volume, analysis of end-tidal CO2, transcutaneous O2 and CO2 measurement and blood gas analysis. These methods are evaluated and their limitations discussed. Special attention is paid to the application of these methods used in the different paediatric anaesthetic systems. A three graded plan which classifies the risks for the patients and/or the operations is presented in order to rationalize the use of these methods, some of which require expensive equipment. The basic ventilation monitoring includes, even for short operations in healthy patients (Grade I), the precordial stethoscope, the measurement of the inspiratory oxygen concentration, the measurement of the ventilation pressure and, for school age children also measurement of the expiratory volume. For operations lasting longer than one hour (Grade II) end-tidal CO2 analysis should be used when the ventilation-perfusion ratio is undisturbed. Transcutaneous O2 is desirable, but at the present time not accurate for conditions of general anaesthesia. For all high risk patients and/or operations (Grade III), particularly in the neonates, arterial blood gases are indispensable as well as the other methods for monitoring ventilation.