Laryngeal chemoreflexes (LCR) are triggered by the contact of liquids with the laryngeal mucosa. In the mature organism, LCR trigger lower airway protective responses (coughing, effective swallowing and arousal) to prevent aspiration. General belief holds that LCR are responsible for apnea and bradycardia in the newborn mammal, including humans. We have recently shown that LCR in full term lambs are consistently analogous to the mature LCR reported in adult mammals, without significant apneas and bradycardias (29). The aim of the present study was to assess LCR in nonsedated, newborn preterm lambs born at 132 days of gestation (term = 147 days). The preterm lambs were instrumented for recording glottal adductor EMG, EEG, eye movements, heart rate, respiration and oximetry. A chronic supra-glottal catheter was used for injecting 0.5 ml of saline, distilled water and HCl (pH 2) during quiet sleep, active sleep and wakefulness on postnatal day 7 (D7) and 14 (D14). Laryngeal stimulation by water or HCl on D7 induced significant apneas, bradycardia and desaturation, which, at times, appeared potentially life-threatening. No significant apneas, bradycardias or desaturation were observed on D14. No consistent effects of sleep state could be shown in the present study. In conclusion, laryngeal stimulation by liquids triggers potentially dangerous LCR in preterm lambs on D7, but not on D14. It is proposed that maturation of the LCR between D7 and D14 is partly involved in the disappearance of apneas/bradycardias of prematurity with postnatal age.