Take a disease of complex pathology with inflammatory and neoplastic features, which affects lymphoid and neural tissues, belonging to a disease group which killed one chicken in five, and which defied efforts to understand and control it for lOre than 50 years, and one can begin to appreciate the interest Marek's disease has received. Canpound these characteristics with the finding of the causal herpesvirus, its recog nition as the neoplasm first discovered to be so caused, and its pre vention by vaccination, and the special place of Marek's disease in veterinary medicine and comparative...