Increasingly. the role of immunologic mechanisms in the etiology and progression of neurologic diseases, particularly those involving demyelination, is being recognized. In appreciation of this, the Rockefeller Foundation recently convened a small group of neurologists and immunologists to exchange their views not only with respect to pathogenesis, but also with emphasis on the application of immunologic modalities to the treatment of these diseases. Among the participants was Sir Peter B. Medawar, Nobel Laureate, of the Medical Research Council, Clinical Research Centre at Harrow, England.The following special report on the conference in Bellagio. Italy, was prepared by Dr. Medawar.