A study was made of the influence of geomagnetic storms at the latitude of Moscow on the electric activity of the human cerebral cortex. By electroencephalographic measurements it was shown that when volunteers aged 18–23 were performing tasks on a computer during moderate magnetic storm or within 24 h after it, the values of the coherence function for electric oscillations in the frontal-polar and occipital areas of the brain in the 4.0–7.9 Hz range (theta rhythm) decreased by a factor of two or more (relative to quiet geomagnetic conditions), whereas the arterial blood pressure, respiratory rate and the electrocardiogram registered in parallel did not deviate from the norm.