XMRV detection Mark James Robinson, Jefferiss Trust Laboratories, Imperial College London 29 November 2011 Dear Sir, You state in your discussion that "Of the remaining 27 publications, 13 studies used Taq or master-mixes likely containing UNG (it was present in 8 studies [2-9] and possibly used in the remaining 5 studies [10-14] that we examined" As authors of study , we would like to clarify that we did not use UNG in our master mix as indicated in the methods section of our publication. We were able to show that our PCR was highly sensitive. Furthermore, we have been able to detect traces of contaminating murine DNA by nested PCR in several publications (see references below), indicating that PCR inhibition is not an issue in our assay. References Robinson et al. Retrovirology 2010, 7:108 Erlwein et al. PLoS One 2011, 6(8):e23484 Competing interests We are the authors of reference .