Several techniques exist for assessing chest wall movements in children, that incorporate different measurement principles. Although the output from such devices appears very similar, the comparability of data from different devices needs to be evaluated. We have investigated the simultaneous measurement of chest wall movement using three different devices in 12 children recovering from intensive care. The devices used were inductance plethysmography (assessing thoracic cross-sectional area), magnetometers (assessing thoracic diameter), and a Hall device strain guage (assessing thoracic circumference). Measurements of respiratory timing and of phase angle between rib cage and abdomen in these patients showed a close agreement between devices in ventilated patients. However, occasional inconsistencies occurred in patients who were breathing spontaneously. We suggest that it may not always be appropriate to directly compare data on chest wall movements in children recorded using different measurement techniques. The best method of measurement varies with the clinical picture.