OBJECTIVES: The aim of the study was to assess the mechanism of cardiovascular impairments in workers exposed to UHF-VHF radio frequency electromagnetic fields (EMF). MATERIALS AND METHODS: Heart rate variability (HRV) was analysed using 512 normal heart beats registered at rest. The analysis concerned time-domain (STD R-R) and frequency-domain (VLF, LF, HF) parameters of HRV. Fifty nine workers (group I) with low-level and 12 workers (group II) with high-level exposure were examined. The mean age of the subjects was 47 +/- 9 years and 41 +/- 14 years, and mean exposure duration 19.1 +/- 8.8 years and 13 +/- 4 years, in groups I and II, respectively. The groups were divided according to: E(max), E(dose), E(mean) for frequencies UHF, VHF and UHF+VHF: The control group consisted of 42 non-exposed subjects, aged 49 +/- 8 years. Statistical analysis comprised one-way analysis of variance, covariance analysis and logistic regression models. RESULTS: In the exposed groups, the heart rate was higher than in the control one. Standard deviation of R-R intervals (STD R-R) was found to be significantly (p = 0.0285) lower in group I (42.5 +/- 24.7 ms) compared to the control group (62.9 +/- 53.5 ms). The risk of lowered STD R-R was significantly increased (OR = 2.37, p = 0.023) in group II. Both exposed groups presented significantly higher VLF and LF values than the control group (p = 0.005 and p = 0.0025, respectively). The EMF-exposed groups were characterised by the dominance of the sympathetic system (LF/HF 1.3 +/- 0.35). CONCLUSIONS: The results indicate that exposure to radiofrequency EMF may affect the neurovegetative regulation.