Background. Bioelectrical impulses, also known as brain wave rhythms, have been known for years to correspond with mental activities. Thus an electroencephalogram can produce concrete information regarding both the physiological status (alertness, sleepiness) and emotional status (tension, relaxation) of the subject, since these states are associated with particular bioelectrical patterns. The purpose of our study was to examine the effects on low-frequency magnetic fields on the amplitudes of bioelectrical activity in the cerebral hemispheres, as registered by EEG. Material and methods. EEGs were performed on 92 women, 21-23 years of age, in the Clinical Psychology and Psychophysiology Laboratory at the Maria Grzegorzewska Academy of Special Education in Warsaw. The subjects received low-frequency magnetic field stimulation or a placebo while performing cognitive tasks. All the subjects were examined 6 times to determine the behavior of alpha, beta, SMR, theta, and delta waves after magnetic stimulation. The results were recorded on-line from the F3 -C3 (left hemisphere) and F4-C4 (right hemisphere) leads. Results. Statistical analysis shows that low-frequency magnetic fields, regardless of hemisphere, have a positive effect on the amplitudes of the tested brain waves. Conclusions. In comparison to the right hemisphere, the low-frequency magnetic fields generated by the Viofor JPS device much more markedly improve the functionality of the left hemisphere, known as the „logical” hemisphere.