Limitations in home monitoring technology have precluded longitudinal studies of hemoglobin oxygen saturation during unperturbed sleep. The memory monitor used in the Collaborative Home Infant Monitoring Evaluation addresses these limitations. We studied 64 healthy term infants at 2 to 25 weeks of age. We analyzed hemoglobin oxygen saturation by pulse oximetry (SpO(2)), respiratory inductance plethysmography, heart rate, and sleep position during 35, 127 epochs automatically recorded during the first 3 minutes of each hour. For each epoch baseline SpO(2) was determined during >/=10 s of quiet breathing. Acute decreases of at least 10 saturation points and <90% for >/=5 s were identified, and the lowest SpO(2) was noted. The median baseline SpO(2) was 97.9% and did not change with age or sleep position. The baseline SpO(2) was <90% in at least 1 epoch in 59% of infants and in 0.51% of all epochs. Acute decreases in SpO(2) occurred in 59% of infants; among these, the median number of episodes was 4. The median lowest SpO(2) during an acute decrease was 83% (10th, 90th percentiles 78%, 87%); 79% of acute decreases were associated with periodic breathing, and >/=16% were associated with isolated apnea. With the use of multivariate analyses, the odds of having an acute decrease increased as the number of epochs with periodic breathing increased, and they lessened significantly with age. We conclude that healthy infants generally have baseline SpO(2) levels >95%. The transient acute decreases are correlated with younger age, periodic breathing, and apnea and appear to be part of normal breathing and oxygenation behavior.