RESUMO
The structural protein of murine tumour virus P30 has been measured by radioimmunoassay. The titer of each serum was determined by using as antigen the purified Rauscher viral protein labeled with 125iodine. Standard competition curve was constructed in order to determine the equivalent of protein to inhibit the precipitation reaction under limited antibody concentration. Competition by purifed Kirsten virus suspension, normal rat kidney cells, transformed-productive and transformed non-productive cells were measured in homologous and heterologous system. Type, group and interspecies determinants were characterized using the proper antigen-antibody system. Once the proteins have interspecie determinants, it is possible that we might be able to use some mammalian virus protein as tool to determine the presence of viral protein in human processes.