My thoughts on these two types of studies Replication vs Validation Studies - the Imperial College and CD tests are validation 'studies' not replication studies and there's a big difference between them. Replication studies follow the first studies techniques to the letter.They're using the same processes to find the same genetic sequences that the original study found. Validation studies, on the other hand, simply try to validate the first studies assertion - in this case the WPI's assertion that they found XMRV. They're not trying to replicate the original techniques; in fact, it's better if they don't. Virus hunters can use any number of techniques to find a virus; if a virus is there any of these techniques should be able to find it. Thus, they're often using different kinds of PCR tests and are often looking for different genetic sequences than in the original study. When Imperial College or CD attempts to detect the virus using a different means than the WPI does, its trying to validate their assertion that they've found XMRV - not find the same genetic sequences WPI did. Notice that the WPI did not take Imperial College to task for saying whether or not they found XMRV - they took them to task for not replicating their results. In order for them both to be right WPI must have found something a bit different from XMRV - a possibility - or one of the two groups made a mistake. Given that the WPI was working with 2 other important labs - if a mistake was made I would suggest it was probably Imperial that made it. I would think the most probable conclusion, though, was that they both did their tests right and WPI found something different than what Imperial was looking for: ie standard XMRV. (How standard XMRV is is in question since it was undoubtedly gleaned from a few prostate cancer samples. ) The Science Paper - Thank god the Science Journal pushed them so hard because if studies start rolling in showing that no one can find 'XMRV' the whole thing could concievably crash to a halt right there with the research community believing it was nothing but a contaminant. But the WPI showed that if you put an infected cell next to an uninfected cell that uninfected cell gets infected - and contaminants, by default - broken up bits of endogenous retroviruses - cannot, to my knowledge, infect other cells. That makes it intriguing for retrovirologists and hard to dismiss their findings even if labs cannot find 'XMRV'. Something in their slides was infecting cells - and that appears to be quite unusual.