Static and 60 Hz magnetic fields, 0.78 gauss, were applied individually and combined to each of 20 human subjects during 2 sec epochs, and the effect on the EEG was determined by comparing the power spectrum obtained during field exposure with that from control epochs. All but one subject exhibited field-induced alterations in the EEG; most subjects exhibited increased EEG activity at 2 or more frequencies within 1-18.5 Hz. The field-induced changes were recorded more often at the central and parietal electrodes than at the occipital electrodes. The responses observed during application of combined static and alternating fields did not differ from the sum of the responses observed when the fields were applied individually, even though the exposure conditions were specifically chosen to favor the hypothesized ion-resonance mechanism of interaction involving Ca2+. The data support the view that detection loci for magnetic fields exist within the nervous system.