Twenty-four-hour tape recordings of ECG and breathing movements from 16 term infants (greater than or equal to 37 weeks' gestation) who subsequently died of sudden infant death syndrome (SIDS) were compared with recordings from surviving infants from the same populations. Apneic pauses of varying durations, periodic and regular breathing patterns, heart and respiratory rates during regular breathing were measured. Only one of 16 full-term infants with SIDS had findings outside the range of age-matched control infants (an excess of periodic breathing patterns and an absence of regular breathing). When the first recordings of each of infants who died of SIDS, except one who had cyanotic episodes prior to death, were compared to recordings of survivors (six for each case) closely matched for age, gestation, and weight at birth, no differences in breathing patterns or heart or respiratory rates during regular breathing could be demonstrated. These particular measurements of cardiorespiratory function were, therefore, unable to identify the majority of full-term infants at risk for SIDS.