EMB and myalgic encephalomeyelitis/chronic fatigue syndrome: To remove any element of doubt, we have repeated our genetic analysis using the same oligonucleotide primer sets described in [10] and, in addition, we have assayed sera taken from 130 of our CFS patients and 30 normal healthy subjects (NHS) for antibodies to the New Zealand Black (NZB) xenotropic virus and its envelope protein, gp70, a virus that shares more than 94% overall homology with XMRV.