The relationship of sleep apnea to age, sex, and Alzheimer's dementia was investigated in 45 elderly subjects and 10 young males, all nonobese, normotensive, nonsmoking, with no sleep complaints and no medical problems other than Alzheimer's disease. Mean apnea/hypopnea index [(AH)I] was significantly greater in elderly males than in young males or elderly females. Mean (AH)I and percentage of subjects with an (AH)I greater than 5 in the Alzheimer groups were not significantly different from age and sex-matched controls. Results were similar when the apnea index was substituted for (AH)I. The data from this preliminary study indicate that healthy, elderly males with no sleep complaints and elderly males with Alzheimer's disease experience a significant, subclinical ventilatory impairment during sleep. Data from the 10 elderly females and 10 young males indicated no such impairment. The physiological significance of this degree of sleep apnea in otherwise healthy elderly males is unclear at present.