We have previously shown that children (average age 9 yrs) with mildly elevated obstructive apnoea/hypopnoea indices (OAHI) retained CO(2) at rest. Here, we report the results of a 6-yr follow-up study on 14 children from that study. Minute ventilation (V'(E)) and end-tidal CO(2) partial pressure (P(ET,CO(2))) were measured during hypercapnic challenge. OAHI decreased from 7.5+/-4.7 events x h(-1) at age 9 yrs to 2.5+/-1.8 events x h(-1) at age 15 yrs (p<0.001), despite an increase in body mass index from 20+/-4.6 kg x m(-2) to 26+/-5.7 kg x m(-2) (p<0.0001). Eupneic V'(E) increased from 4.1+/-0.31 L x min(-1) x m(-2) to 5.9+/-0.4 L x min(-1) x m(-2) (p<0.01), while P(ET,CO(2)) fell from 44.1+/-0.8 to 33+/-1.0 mmHg (p<0.001). The V'(E)-P(ET,CO(2)) obtained during hypercapnia was left shifted, such that V'(E) at a P(ET,CO(2)) of 50 mmHg increased from 24 L x min(-1) at age 9 yrs to 36 L x min(-1) at age 15 yrs. Central respiratory drive did not change. We hypothesise that somatic growth of the pharynx coupled with a regression of tonsillar tissue mass with age leads to enlargement of the upper airway lumen, a reduction in airway resistance and increased respiratory airflow at a given level of ventilatory drive.