&NA;The extent of a brain tumor or abscess in the cerebral hemispheres can be easily projected onto the scalp by using small radioactive markers. A positive uptake by the lesion is seen on the persistence scope of the nuclear camera and can be delineated by scalp markers to define the limits of future craniotomy. This technique has been used for six tumor operations and has successfully reduced the size of the craniotomy and brain incision, as well as increasing the accuracy of localizing the tumor.