The ventilatory response to anoxia in unanaesthetized rat pups of 1 and 8 days of age was studied. Ventilation was recorded by barometric plethysmography. During acute anoxia (100% N2), animals of both ages responded with hyperpnoea, primary apnoea, hypoxic gasping and secondary apnoea. After secondary gasping, occasional gasps occurred. If oxygen was administered during the gasping period, all animals survived through autoresuscitation. The duration of the period of hypoxic gasping was significantly longer in the 1-day-old animals. Adrenalectomy reduced the length of this period in both 1- and 8-day-old animals. In a second series of experiments, the effect of adrenergic antagonists on autoresuscitation was examined. Pretreatment with the non-selective alpha-receptor antagonist phentolamine reduced the duration of gasping in 1-day-old rats, but prolonged this duration in 8-day-old rats. The non-selective beta-receptor antagonist propranolol did not affect the duration of gasping in 1-day-old rats, whereas it prolonged this period in the older animals. We conclude that proper duration of gasping during anoxia is dependent on intact adrenal function and that the adrenal glands therefore play an important role in autoresuscitation from anoxia during postnatal life. The underlying mechanism appears to involve alpha-adrenergic receptors.