There is a relationship between deficient sleep arousal response to asphyxia, the presence of symptomatic apnea, and the risk for recurrent episodes of life-threatening sleep apnea. This documented abnormality in arousal responsiveness, which could result in the inability to respond to apnea-induced asphyxia, is the only respiratory control deficit that could result in sudden death. Inability to arouse from sleep in response to asphyxia may also be the underlying abnormality explaining numerous other behavioral deficits reported in infant groups with symptomatic apnea or otherwise thought to be at increased risk for sudden infant death syndrome (SIDS), including awake behavioral differences in temperament. An arousal response deficit to asphyxia may thus be a critically important and fundamental pathophysiological component of the essential defect necessary for the occurrence of sudden death during sleep. As with any other observed abnormality, however, it has not yet been possible to design an asphyxic arousal response test with sufficient accuracy and sensitivity to identify prospectively those infants otherwise destined to die of SIDS. Although an impairment in arousal responsiveness may be necessary for SIDS to occur such a deficit may not be sufficient to cause SIDS unless or until another factor(s) occurs that can cause sleep-related asphyxia. Although impaired respiratory control appears to be the likely precipitating cause of sleep-related asphyxia, it is also possible that factors unrelated to respiratory control are important in causing asphyxia; superimposed on an underlying arousal deficit, these could result in SIDS.(ABSTRACT TRUNCATED AT 250 WORDS)