In the absence of a specific XMRV serological assay, we made use of an ELISA in which Goat anti-Rauscher MLV gp70 and goat anti-NZB xenotropic virus antibodies were employed to detect gp70 Env protein in sera of CFS patients. The gene discussed is ERVW-1; the disease is myalgic encephalomeyelitis/chronic fatigue syndrome.