INTRODUCTION: Parathormone (PTH) is a very potent uraemic toxin, which affects heart structure and function. PTH also plays the role in uraemic autonomic neuropathy (AN). The aim of the study was to investigate the relationship between high PTH level and AN assessed with frequency domain measures of heart rate variability (HRV). MATERIALS AND METHODS: A 24-h ECG was performed in 40 HD (F=19, M=21) patients aged 49+/-11 years, duration of HD therapy 37+/-30 months. Frequency domain measures of HRV were obtained according to European Society of Cardiology recommendations. Total spectral power (TP), high frequency band (HF) and low frequency band (LF) were computed as indexes of: total autonomic nervous system (ANS) activity, parasympathetic and sympathetic activities, respectively. LF/HF ratio was calculated. TP, HF, LF and LF/HF were expressed as natural logarithm. Patients were divided into two groups due to PTH level: PTH+ (PTH> or =275 pg/ml) and PTH- (PTH<275 pg/ml). RESULTS: The values of lnTP and lnLF were lower in patients PTH+ than in patients PTH- (6,58+/-0,76 vs. 6,99+/-0,44 ms2, p<0,05, and 4,91+/-0,99 vs. 5,33+/-0,65 ms2, respectively, p=0,06). We also found negative correlation between lnPTH and lnTP (r=-0,47; p<0,005), lnPTH and lnLF (r=-0,35; p<0,05), lnPTH and lnHF (r=-0,34; p<0,05). On multiple regression analysis, lnTP, lnLF and lnHF were independently related to lnPTH. CONCLUSIONS: Parathormone exerts effect on activity of both parts of autonomic nervous system: sympathetic and parasympathetic. High PTH level deteriorates total autonomic activity.