The authors studied sleep organization and modifications in ventilation in 20 healthy subjects (11 men, 9 women) with an average age of 65 years. There was a diminution (in relation to young adults) in the quantity of sleep with a relative increase in light slow wave sleep and reduction in deep slow wave and REM sleep phases. A reduction was also noted in the ventilation rate during slow wave and REM sleep phases in relation to calm awake periods, especially towards the end of the night. This was due to a reduction in tidal volume insufficiently compensated by an increased ventilation frequency. Hypopnea and apnea were noted in 19 of the 20 subjects, the latter occurring in the form of obstructive apnea during light slow wave sleep. The variable number of apnea can be used to divide the subjects into two sub-groups: one group of 14 of the subjects who had less than 50 apnea; the other group containing 6 subjects, all males, having more than 80 apnea during the night, and being identical to a group of patients with the sleep apnea syndrome.