Cortical sensory potentials have been evoked under general anesthesia by median nerve stimulation and direct cortical stimulation of the motor cortex in 35 consecutive patients with mass lesions in the middle half of the cerebral hemispheres. The evoked potentials produce movement that is useful in localizing the pre- and postcentral gyri. Ultrasound has also been used to aid in the selection of access routes to subcortical lesions while sparing the cerebral cortex bordering the rolandic fissure. In five of these 35 patients, the sensory evoked response was also monitored throughout selected portions of their operative procedures. Representative cases have been presented to illustrate how observations made with these methods have been used to facilitate the patient's intraoperative management in an effort to limit postoperative morbidity.