This study aimed to determine whether preterm infants who have a history of apparent life-threatening events (ALTE) have abnormalities in oxygenation and, if so, whether the ALTE would stop with oxygen therapy. We assessed 92 patients (median gestational age at birth, 32 weeks (range, 24 to 36 weeks); median birth weight, 1840 gm (650 to 3500 gm)) who had had a single (n = 20) or recurrent ALTE. Median postnatal age at referral was 3.2 months (0.5 to 44.7 months). All had been considered otherwise free of symptoms and adequately oxygenated in air at the time of discharge from their neonatal unit, before the ALTE. Fifty-two patients had received mouth-to-mouth resuscitation, and 40 vigorous stimulation. Ninety-one patients underwent 8- to 12-hour recordings of arterial oxygen saturation, the plethysmographic waveforms from the oximeter, breathing movements, and electrocardiograms. These recordings were compared with previously published data from 110 "healthy" preterm infants made at around 6 weeks after discharge from hospital. Compared with these data, 49 recordings (54%) were normal, 19 showed abnormal hypoxemic episodes, 6 had abnormally low baseline arterial oxygen saturation (< 95%), and 17 had both. In 31 of 33 patients, ALTE stopped or were reduced in frequency or severity after additional inspired oxygen (0.1 to 1.0 L/min via nasal cannulas) was given. Oxygen was given for a median duration of 3.9 months (range, 0.8 to 17.2 months). Persistent events in the remaining two patients were subsequently found to be due to intentional suffocation in one and epileptic seizures in the other. Monitoring of transcutaneous oxygen tension at home was undertaken in 84 patients. To date, this has been discontinued in 81 after a median duration of 7.3 months (0.3 to 18.9 months). We conclude that recognition and treatment of abnormalities in episodic or baseline hypoxemia may reduce the risk of further ALTE in previously preterm infants.