The brain-generated currents that produce potentials measured by the electroencephalogram also produce magnetic fields which can be measured by the magnetoencephalogram (MEG), N 20 compatible evoked field after median nerve stimulation is known to be generated in primary sensory cortex. Using MEG with 37 channel SQUIDs, a current dipole is back traced which corresponds to the sensory cortex. When the dipole is projected onto the MRI of the same patient, the primary sensory cortex is precisely identified in the MRI images. These data were used as the key images for navigator enabling a surgeon identify the central cortex in the surgical field. Seven patients with peri-central mass lesion (3 meningiomas, 1 metastatic tumors, 1 angiomas, 2 gliomas) underwent surgery under MEG-navigator method. In every case, the central sulcus and motor cortex were easily identified on the cortex and the tumor was removed as far as possible preserving the motor strip. There were no postoperative worsening of the motor paresis and no other complications were noticed. The method which combines the MEG functional mapping and navigator was considered to be a powerful tool in surgery of the pericentral mass lesions.