In order to measure epileptic seizure(ES)-induced hypoxaemia and explore its relation to other physiological changes, 53 seizures were documented in 10 children (aged 1 week to 5 years) during continuous recordings of breathing, ECG, oxygenation and EEG. Hypoxaemia was demonstrated in 42 ESs with an arterial oxygen saturation (SaO2) below baseline for a median duration of 100s and < or = 60% for 17s, despite resuscitation. There were pauses in breathing movements in 45 seizures, but only 35 of these were hypoxaemic; pauses of comparable severity occurred in the 10 seizures without hypoxaemia. In seven seizures there was hypoxaemia without pauses in breathing movements, although continued nasal airflow was not demonstrable. Sinus tachycardia occurred in 35 seizures and T-wave changes in 20, but no sinister arrhythmias were observed.