Despite evidence that respiratory control mechanisms may be altered in infants who succumb to the sudden infant death syndrome (SIDS), overall respiratory variability in SIDS victims is comparable to that of control infants. We assessed dynamic characteristics of breathing in 16 recordings of apparently healthy infants who subsequently died of SIDS, and 35 recordings of age-matched control infants. Each breath-to-breath interval in 10-min epochs of quiet sleep and rapid eye movement sleep was plotted against the previous interval. Dispersion of next-intervals was determined after short, intermediate, and long interbreath intervals. In SIDS victims, dispersion after long intervals (slow respiratory rates) was significantly restricted relative to control infants. Moreover, after long breath-to-breath intervals, SIDS victims showed smaller mean breath-to-breath changes in respiratory rate than did controls. The findings indicate that breath-to-breath respiratory patterns differ in infants who succumb to SIDS, and the differences occur preferentially at low respiratory rates.