A 4-yr-old girl with a ganglioglioma involving the cerebellum and pons presented with CO2 retention and arterial O2 desaturation during wakefulness and sleep. Despite the presence of a regular respiratory pattern during wakefulness, NREM sleep was associated with the appearance of a sustained periodic respiratory pattern characterized by clusters of usually two breaths separated by an 8 to 10-s expiratory pause. At sleep onset, this Biot's respiratory pattern appeared immediately after a sigh. Breathing frequency during NREM sleep became regular with administration of supplemental O2 and an attendant increase in end-tidal CO2. Shortly after withdrawal of supplemental O2 during NREM sleep, the periodic pattern resumed and was again immediately preceded by a sigh. The observations during NREM sleep in this patient with a central nervous system abnormality indicate that Biot's type respiratory pattern may be reversed by administration of supplemental oxygen. The results in this patient suggest: (1) the presence of a very elevated CO2 apnea threshold, and (2) that the pons may play a role in determining the effect of hypercapnic hypoxia on respiratory pattern during sleep.