In this study One lymph node from cow with viral lymphosarcoma and one lymph node from healthy cow were analyzed by three different methods for protein extraction, include simple homogenizing in PBS, sonication and phenol extraction. Tumor antigen detection relies on immunoprecipitation followed by SDS-PAGE. In this experiment Streptococcus pyogenes was used for purification of immune complexes. Eletrophoretic patterns were obtained using reduced and non reduced buffers. In PBS homogenization 3 distinct antigens (39, 32 and 30 kDa) were observed. When sonication or phenol extraction were used, 5 (72, 48, 42, 32 and 30 kDa) and 6 (104, 77, 54, 32, 30 and 26, 5 kDa) distinct antigens were observed, respectively. This study showed that the ability of antigen detection mainly depends on protein extraction procedure and antigen-antibody equilibrium achieved by quantification of precipitins. Immunoprecipitation could be used successfully for study of tumor antigens in bovine leukosis.