Diminished heart rate (HR) variability has been reported in patients with early phase Parkinson's disease (PD) using standardized cardiovascular reflex tests. However, limited data exist on HR variability during sleep; thus the present study was performed to investigate the characteristics of HR variability during different sleep stages. The HR variability of 21 newly diagnosed and untreated PD patients and of 22 control subjects was evaluated by using time domain, frequency domain and non-linear methods and by analyzing HR reactions to body movements during the different sleep stages (non-REM stages S1-4 and the REM stage). The nocturnal cardiac autonomic control was disturbed in PD patients compared to controls both during sleep and waking. HR reactions to body movements were decreased especially during REM sleep referring to defective sympathetic cardiovascular control. High frequency spectral power of HR variability was attenuated in the patients in waking and during non-REM sleep but not during REM sleep suggesting that parasympathetic cardiovascular control is also affected in early PD. However, the variance of R-R intervals during non-REM sleep was significantly increased in PD patients. Especially during this sleep stage the patients also moved more than the controls. HR variability is decreased not only in waking but also during sleep in PD patients. However, the increased variance of HR during non-REM sleep refers that in early phase of PD cardiovascular system is still able to react to changing body circumstances. Furthermore, our findings suggest that the indicators measuring the dominant sympathetic or parasympathetic activity of each given sleep stage are the most sensitive measures in revealing disturbed nocturnal ANS function.