The genetic revolution is now well underway. Hardly a week goes by without researchers announcing that they have mapped another part of the human genome. As a result, researchers looking for new therapeutic targets for gene therapies are almost spoilt for choice. However, while the gene therapy revolution may seem unstoppable, the first casualties were recently reported. There are growing concerns over safety, highlighted by the death of 18-year-old Jesse Gelsinger during a recent clinical trial in the US. Researchers now face increasing scrutiny - in the US, at least. Moreover, there are doubts about whether outcome measures employed in conventional trials apply to some gene therapy studies.