In preterm infants, reliance on the detection of apnoeic pauses and/or bradycardia results in significant amounts of hypoxaemia remaining undetected. In addition, recordings of breathing movements and ECG do not have predictive value for subsequent sudden infant death. In recent years, the ability to continuously monitor and record arterial oxygen saturation (SaO2) has produced important information regarding the mechanisms for respiratory events in the preterm population. Normal data on SaO2 (Nellcor N-200) and breathing movements have been collected in 160 preterm infants. Median baseline SaO2 during regular breathing was 99.5% (range 88.7-100) at the time of discharge from SCBU and 100% (95.3-100) at follow-up 6 weeks later. Episodic desaturations (SaO2 < or = 80% for > or = 4 s) ranged between 0 and 355 episodes per 12-hour recording. In a study of a separate group of 16 preterm infants with recurrent cyanotic episodes of unknown cause, the total number of abnormal hypoxaemic episodes was markedly increased. These hypoxaemic episodes were associated with three breathing pattern: (i) absent breathing movements; (ii) continued breathing movements, but absent airflow, and (iii) continuous airflow and breathing movements. Thus, preterm infants with cyanotic episodes have an increased number of clinically unapparent hypoxaemic episodes, some of which occur with continued breathing and airflow. In another study of 79 patients who had been born preterm and had a history of an apparent life-threatening event, 43 (54%) had abnormal oxygenation on multichannel recordings, including 23% with clinically undetected baseline hypoxaemia.(ABSTRACT TRUNCATED AT 250 WORDS)