Thanks omerbasket. I assume that the WPI also test their cell lines for contamination from XMRV, before they expose it to XMRV+ patient samples. What I don't quite understand is how anyone can test XMRV positive samples for mouse contamination if XMRV is made up from a combination of endogenous mouse viruses. Surely contamination tests would always test positive if XMRV was present, due to the composition of the XMRV DNA/RNA? Do you know if 'one other method' includes the sequencing of the PCR product?