The association between JSRV and human lung cancer is controversial; however, we have demonstrated the presence of an antigen that cross-reacts with a monoclonal antibody specific for the JSRV Env protein in human lung tumors and have amplified env- and gag-like sequences from these samples raising the possibility that JSRV could potentially contribute to lung tumorigenesis in humans. Here, ERVW-1 is linked to lung carcinoma.