The leukosis/sarcoma (L/S) group of diseases encompasses a variety of transmissible benign and malignant neoplasms of chickens caused by members of the family Retroviridae [1]. The term “leukosis” embraces several different leukemialike proliferative diseases of the cells of the hemopoietic system due to avian leukosis virus (ALV), with an undertone that a leukemic blood picture is not always present [2,3]. The components of the hemopoietic system that may undergo neoplastic change include the lymphopoietic (lymphocytic) system, the erythropoietic (red cell) system, and the myelopoietic (myelocytic) system. Presenting signs of the leukosis are mostly nonspecic (loss of appetite, weakness, emaciation, diarrhea, pale wattles). Lymphoid leukosis (LL) has been the most common form of L/S group of diseases seen in eld ocks, although more recently, myeloid leukosis has become increasingly prevalent.