Recent reports suggest that sudden infant death syndrome (SIDS) may be related to an inappropriate diving reflex or obligate nose breathing. Immersion of the neonatal monkey's face in cold (14 C) water, or nasal occlusion resulted in apnea which is occasionally persistent, bradycardia, and relative hypertension. In the same monkeys at an older age, apnea never persisted after removal of the diving stimulus, and there was no obligate nose breathing. The study documents a dive reflex and obligate nose breathing and concludes that the infant monkey is a suitable model for the study of SIDS. We suggest, however, that the fatal factor in crib death may be the failure to interrupt apnea however the apnea was initiated. The failure to resume respiration may represent an inappropriate return to the apneic state of the fetus.