Sixteen healthy term infants underwent 12 hour tape recordings of arterial oxygen saturation (SaO2)(Nellcor N100 in beat to beat mode) and breathing movements at around 6 weeks, 3 and 6 months of age. Six of these infants had an additional recording at around their first birthday. Recordings were analysed throughout for pauses in breathing movements of greater than or equal to 4 s (apnoeic pauses), episodes in which SaO2 fell to 80% (desaturations), and (only during regular breathing) baseline SaO2. In the 16 infants studied at 6 weeks, 3 and 6 months, the median frequency of both apnoeic pauses (5.6, 5.7, and 6.1/h, respectively) and desaturations (0.7, 0.4 and 0.5/h, respectively) showed little change. The majority of desaturations followed an apnoeic pause (median 73.2, 86.2 and 93.8% of desaturations). The median proportion of apnoeic pauses followed by a desaturation did not change significantly (9.0, 7.5 and 9.1%), despite an increase in the proportion of apnoeic pauses of greater than or equal to 8 s in duration from 2.0% at 6 weeks to 5.3% at 3 months (P less than 0.01). Baseline SaO2 was 97.3% or higher in all recordings. Median baseline SaO2 increased from 99.6 to 99.9% between 6 weeks and 3 months (P less than 0.02) and remained unchanged thereafter. In the subgroup of infants studied also at one year of age, again no significant differences were found with increasing age in the frequency of either apnoeic pauses or desaturations. The data show that in healthy subjects no major changes occur between 6 weeks and 1 year of life in apnoeic pause frequency or arterial oxygenation.(ABSTRACT TRUNCATED AT 250 WORDS)