The present study describes a device (AMD43) for ambulatory measurement of respiration rate and respiratory sinus arrhythmia from the combined electrocardiogram (ECG) and thoracic impedance signals. Respiratory time intervals derived from this ambulatory device closely corresponded to those derived from simultaneous recordings with a ‘classical’ laboratory set-up. Good cross-instrument comparison was also found for respiratory sinus arrhythmia parameters derived with both the peak-to-trough and spectral analyses methods. It is discussed how simultaneous measurement of respiration rate, respiratory sinus arrhythmia may be used to asses cardiac vagal tone in real-life situations.