The contribution of the carotid body chemoreceptor to postnatal maturation of breathing was evaluated in lambs from 7 to 70 days of age. The study was conducted by comparing the eupneic ventilation and resting pneumograms in intact conscious lambs with those of lambs that were carotid body chemodenervated (CBD) at birth. In comparison to the 1-wk-old intact lambs, the CBD lambs had significant decreases in minute ventilation (VE, 313 vs. 517 ml/kg), tidal volume (VT, 7.2 vs. 10.5 ml/kg), respiratory rate (f, 44 vs. 51 breaths/min), and occlusion pressure (P0.1, 2.8 vs. 7.2 cmH2O). Arterial PO2's were 59 vs. 75 Torr (P less than 0.05) and arterial PCO2's 47 vs. 36 Torr (P less than 0.05), respectively, in CBD and intact lambs. In intact lambs from 7 to 70 days, resting VE decreased progressively from 517 to 274 ml/kg (P less than 0.01) due to a fall in VT, mean inspiratory flow (VT/TI), and f, whereas the ratio of inspiratory time to total breath duration remained constant. P0.1 decreased from 7.2 to 3.9 cmH2O from 7 to 42 days. In contrast the CBD lambs experienced only minimal changes in VE, VT, VT/TI, and f during the same period. VE only decreased from 313 to 218 and P0.1 from 2.8 to 2.4 cmH2O. In contrast to that of intact lambs the resting pneumogram of CBD lambs remained relatively fixed from 7 to 70 days. Three CBD lambs died unexpectedly, without apparent cause, in the 4th and 5th wk of life.(ABSTRACT TRUNCATED AT 250 WORDS)