Sleep-related hypopneas and apneas were studied in 19 patients with multiinfarct dementia (MID), in 21 patients with Alzheimer's disease (AD), and in 26 healthy control subjects using the Static Charge-Sensitive Bed (SCSB) method. Demented patients had more apneas or hypopneas and more disturbed sleep than the control subjects. Over 10 apneas/hypopneas per hour of sleep were detected in 47.5% of the demented patients and in 19.2% of the control subjects (p less than 0.05). Restlessness comprised 46.7% of the time in bed in patients with AD and 49.6% in those with MID, but only 102.% in the control subjects (p less than 0.001, controls versus demented). The total duration of apneas and hypopneas calculated from the total sleeping time was greater than 10% in 60.0% of the demented patients and in 15.4% of the control subjects (p less than 0.001). Patients with MID tended to have more apneas/hypopneas than those with AD, and apneas/hypopneas tended to increase in direct proportion to the severity of dementia. Age had no effect on the proportion of apneas and hypopneas among demented patients or control subjects, but male controls had more apneas and hypopneas than did female controls.