The recently discovered retrovirus, xenotropic murine leukemia virus-related virus (XMRV), has been identified in some prostate cancer patients. In light of conflicting data concerning XMRV, standardized diagnostic testing is important to identify patients in which XMRV is present and to determine whether it plays a role in the incidence of prostate cancer. Researchers now report the successful development of an experimental clinical test for XMRV.