The aim of this study was to examine cardiorespiratory control in infants presenting with an apparent life-threatening event (ALTE). We performed six to eight 45 degrees head-up tilts in 10 ALTE infants (age, 14 +/- 3 weeks) and 12 age-matched control subjects during slow wave sleep and rapid eye movement sleep (REM). All infants underwent full overnight polygraphic sleep recordings with noninvasive measurement of beat-to-beat blood pressure. All control infants had normal sleep breathing. In contrast, 5 of the 10 ALTE infants had more than two obstructive apneas per hour of sleep, with short hypoxic episodes (obstructive sleep apnea OSA). In slow wave sleep, in response to the tilt, the ALTE infants with OSA showed a reduced heart rate response, and three of the five showed a marked postural hypotension. The ALTE infants with OSA also had altered heart rate and blood pressure variability and an increased arousal threshold in REM (p = 0.0002). By contrast, those ALTE infants with normal sleep breathing had cardiovascular and arousal responses similar to those of the control infants. We conclude that a number of ALTE infants with OSA have abnormal cardiovascular autonomic control that, combined with their decreased arousability in REM, may provide an explanation for the ALTE episodes.