Introduction: Transcranial application of weak random noise may appear to be a promising tool for clinical neuroplasticity research, for it allows a painless, selective, focal, non-invasive and reversible excitability modulation of the cortex without an adaptation effect. The “random noise” signal contains all frequencies up to half of the sampling rate, i.e. a maximum of 640Hz. This random level of current is generated for every sample (sampling rate 1280 sps) and is normally distributed; the probability density function follows a bell-shaped curve. Methods: Stimulation was delivered by a battery-driven electrical stimulator (NeuroConn GmbH, Ilmenau, Germany) through conductive-rubber electrodes placed in two saline-soaked sponges. To detect these current-driven changes of excitability we used single-pulse TMS, frequently employed in these kind of studies. The intensity of the TMS pulse is calibrated before the experiment to induce a motor-evoked potential (MEP) amplitude of about 1mV in the resting first dorsal interosseous muscle. MEP size increases or decreases after an external stimulation of the brain reflecting excitability enhancement or reduction of the motor cortex. Following stimulation, 40 single test-pulse MEPs were recorded at a time constant of 4±0.04s eight times, i.e. approximately 0min, 5min, 10min post-stimulation and then every 10min up to 60min. Results: Applying 10-min random noise stimulation over the primary motor cortex induces excitability changes of up to 20–50%, as revealed by TMS, which lasts for 60min post-stimulation. However, RNS over the premotor cortex did not induce any significant excitability changes. The observed increase in MEP post- stimulation indicates that tRNS application has the ability to modulate levels of cortical excitability.