VC measured with a Monaghan electronic spirometer equipped with a backflow valve is significantly lower (about 4%) than when measured with the same spirometer without such a valve. The measurements of FEV1.0 were not influenced by the valve. 73 healthy children were investigated with the Monaghan spirometer equipped with the backflow valve and normal reference data were established. The results were very similar to those obtained in an investigation of healthy children with the same spirometer about one year earlier. Reference data on children for a simple flow meter, Airflometer (Glaxo Ltd.), are given. The data correlated very highly to the FEV1.0 values obtained by the Monaghan spirometer. After inhalation of salbutamol healthy children had a small and significant increase of FEV1.0 and of the Airflometer value but not of VC. The deviations of the differences were small. A 6% increase of VC and 10% increase of FEV1.0 were taken as normal upper limits after inhalation of salbutamol. Corresponding increase of the Airflometer values was 15 arbitrary units for children with body heights 116--145 cm and 21 units for children with body heights 146--175 cm.