The most widely used tests for the investigation of the autonomic nervous system (ANS) functioning measure the heart rate (HR) variations during wakefulness. Most tests have some limitations: they require patient collaboration and can be modified by his or her emotional status. We studied HR variability in relation to body movements during sleep in some neurological diseases. Our method seems to be better than the traditional tests in detecting early cardiac ANS damage, especially when the patient is non-co-operative for ANS evaluation during wakefulness after various stimuli.