BACKGROUND: Patients with hypertension have altered autonomic nervous system function, which are increased sympathetic activity. Transcutaneous Electrical Nerve Stimulation (TENS) is a useful modality for pain control and has also been shown to be effective in the reduction of sympathetic activity in healthy subjects and individuals with cardiovascular diseases. OBJECTIVE: The aim of this study was to verify the effects of transcutaneous electrical nerve stimulation by the evaluation of heart rate variability (HRV) in patients with essential hypertension. METHOD: Twenty-eight patients received an application of low-frequency TENS(4 Hz) n=8, highfrequency TENS (100 Hz) n=10 or placebo TENS n=10 in paravertebral ganglionar region during thirty minutes. RESULTS: After 4 Hz TENS, there was a decrease in the low-frequency (LFn.u.) component (57.71+/-9.46 vs 45.58+/-13.51, p<0.026) and an increase in the high-frequency (HFn.u.) component (33.03+/-13.83 vs 45.83+/-20.19, p <0.05) of HRV. After 100 Hz TENS and placebo, there were no changes in the LF and HF components. No significant differences were found in systolic blood pressure with low-frequency TENS (129.37+/- 15.48 vs 126.69 +/- 15.21, p<0.490). There was an increase, although not significant, with high-frequency TENS (131.00 +/- 15.97 vs 138.75 +/- 25.79, p<0.121) and placebo (133.80 +/- 29.85 vs 134.80 +/- 29.72, p< 0.800). No differences were found in the diastolic blood pressure with low-frequency TENS and placebo, but there was a significant increase in high-frequency TENS (81.00 +/- 11.78 vs 85.65 +/- 13.68, p< 0.018). CONCLUSION: Low-frequency TENS decreases sympathetic nervous system activity and increases parasympathetic nervous system activity and high-frequency TENS increases diastolic blood pressure, when applied on the paravertebral ganglionar region in the hypertensive patients.