Amethod for focal stimulation of the brain by entirely extracranial means is presented. A focal X-ray lesion of cortex was made which reduces the blood brain barrier in that area. Then parenteral penicillin was administered. Penicillin is primarily confined to the vascular space by the blood brain barrier in all parts of the brain except for some leakage into the brain at higher doses. An increased concentration of penicillin is created in the irradiated cortex. The penicillin creates a focal epileptic lesion in the irradiated area. This is an example of radiation-controlled focal pharmacology in the central nervous system.