Objective: Circulatory system complications such as blood pressure fluctuations and arrhythmias often affect the prognosis of patients admitted to critical care medical centers and those requiring intensive care. Elucidating the influence of disease on the autonomic nervous system (ANS) is clinically important. We have conducted research with the aim of devising a novel method to monitor ANS dysfunction caused by disease. Patients and methods: Subjects comprised 12 healthy volunteers (10 men, 2 women; mean age, 35.9 years; range, 26-50 years). After obtaining informed consent from each subject, Allen's test was performed to ensure arterial patency. Absence of problems such as peripheral blood flow disturbance or bleeding diathesis was then confirmed. After subcutaneous infiltration anesthesia of the palmar aspect of the wrist, a 24-gauge micro-electrode was inserted using a technique for invasive indwelling monitoring of arterial pressure. The investigator held and touched the electrode tip against the radial artery wall, detecting micro-action potentials. Each subject underwent a Valsalva maneuver and tilt test, and the induced potential changes were recorded. Results: Testing showed micro-action potentials in 8 of the 12 subjects at rest. On Fast-Fourier Transform (FFT) waveforms, waveform patterns showed peaks at low frequencies, gradually decreasing at integral multiples. Amplitudes of action potentials were clearly increased in 6 subjects with the Valsalva maneuver, and in 7 subjects with the tilt test. Detected micro-action potentials likely represented perivascular sympathetic nerve activity (SNA). Moreover, no complications occurred after testing. Conclusion: The radial artery is often used clinically for invasive catheter insertion for arterial pressure monitoring. In the periphery, we were able to detect micro-potentials thought to represent sympathetic nerve activity. The subjects of this qualitative study were healthy volunteers. In future, adding evaluation of integrated peripheral blood flow and quantifying both integrated waveform (IW) and micro-action potentials (MP), we will be able to verify the significance of this achievement by examining the disease associated with ANS, such as sepsis and spinal cord injury.