The top item on prime-time television news in Germany on 21 November featured a statement from research minister Annette Schavan. She was responding to the publication of two studies in which scientists had reprogammed mature adult human cells to behave in a similar way to embryonic stem cells. The findings, she said, vindicated her preference for adult stem-cell research and reprogramming over work on human embryonic stem cells. After all, who needs embryonic cells if it is possible to flick a switch in skin cells to make them a source of virtually any type of cell for perfectly matched tissue replacement?

In the studies in question, researchers at two laboratories reprogrammed mature skin cells, giving them the characteristics of human embryonic stem cells so that they could be coaxed to differentiate into other cell types, such as neurons or heart cells (K. Takahashi et al. Cell doi:10.1016/j.cell.2007.11.019; 2007 and J. Yu et al. Science doi:10.1126/science.1151526; 2007).

Around the world, opponents of human embryonic stem-cell research such as Schavan have leapt on these results to justify their support of tight controls on the work. But this is exactly the wrong time to constrain research on human embryonic stem cells, which for one thing will be required to help scientists work out how best to coax adult cells into becoming new tissues. Both labs say that they could not have made their breakthrough without the work that has been done on embryonic stem cells.

Stem-cell scientists have acclaimed the latest results, while acknowledging that they represent only a first step, and that many issues need to be resolved before there is any chance of applications in the clinic. James Thomson of the University of Wisconsin-Madison, one of the scientists who first isolated human embryonic stem cells and co-author on one of the recent studies, chose this moment to expand publicly on his qualms about using human embryonic stem cells. And Ian Wilmut of the University of Edinburgh, UK, whose team created Dolly the sheep, the first cloned mammal, says that he is abandoning plans to work on human embryonic stem cells.

Many stem-cell scientists share this general unease, both because of the dilemma of working with embryos and because women must donate eggs for the process, in a highly invasive procedure. But they have nonetheless gone ahead with such work because they see it as scientifically necessary if clinical benefits are to be derived any time soon from our growing understanding of cellular differentiation.

This is exactly the wrong time to constrain research on human embryonic stem cells.

These scientists are not oblivious to the ethical issues and they are not merely indulging personal fascination. They have not denied the importance of doing research on adult stem-cells and reprogramming in parallel. It would be a relief for them if all the scientific problems had been solved in the papers published last week — abandoning work on human embryonic stem cells would allow them to operate with a clear conscience and without having to defend their work all the time.

From the researchers' viewpoint, the debate surrounding human embryonic stem-cell research has some parallels with that on animal research. Many would be delighted to abandon the bureaucracy, cost and general inconvenience of doing contentious work. Where genuine alternatives are available, researchers will grasp them. Just as soon as there is no scientific need to work on embryonic stem cells, researchers will design their experiments to use much easier material. But that moment has not yet arrived.