Ultrasonic generation of focal lesions in the brain of experimental animals and man has a well documented history of achievement. All of the previous studies involving ultrasonically generated focal lesions in brain for human therapy have been done with a section of skull removed. Irradiation has then been conducted through the healed overlying tissues and scalp. Experimental animal studies have involved essentially the same procedure with the exception that the lesioning was performed transdurally with the overlying muscle and scalp drawn back. Recent advances in our understanding of adult human skull acoustic characteristics, particularly in the frequency range from 500 kHz to 1 MHz, have lead to successful experiments involving the production of ultrasonically generated focal thermal lesions or flaws in lucite with excised adult human skull as an intervening barrier. Since these thermal lesions in lucite require dosage conditions rather similar to those needed for the production of focal lesions in brain, this research is concerned with an experimental animal study in which brain lesions will be produced with a variety of excised adult human skulls as intervening barriers. Once the necessary experimental animal research has been conducted to define the limits of the methodology, it should be possible to suggest ways in which the non-invasive transkull production of precisely circumscribed focal lesions could be helpful in human therapeutics. In addition, part of the study involves attempts to visualize the ultrasonically produced transkull focal lesions by transkull ultrasonic visualization techniques.