John Coffin, Professor of Genetics and Molecular Microbiology at Tufts University, studies the molecular biology and evolution of retroviruses. He wrote a commentary (A new virus for old diseases?) that accompanied the publication by Lombardi and colleagues of the finding of the new retrovirus XMRV in patients with chronic fatigue syndrome, and has spoken widely about whether this virus has a causative role in the disease. In this video he expresses cautious optimism about the role of XMRV (and related murine retroviruses) in human disease. Note in particular his statement “While the major XMRV studies to date appear to be well controlled for these problems, extreme caution is necessary”.