Just as the United States and United Kingdom are poised to proceed with tightly controlled clinical trials of xenotransplantation, the Council of Europe has thrown the pig among the pigeons by calling for a moratorium. Pessimists are proclaiming that this spells the death of progress. True, animal models are ultimately no replacement for humans; and the ultimate test of whether a risk of creating new human pandemics exists is to open the door a bit and watch what happens.

But xeno-hype hides the fact that the science is far from the point where it might contribute to easing the organ shortage — the primary justification for pushing ahead. Much basic research remains to be done — and politicians should promise to emphasize that more research is needed every time they mention the moratorium word. There is little good reason to rush into the clinic, even though that would permit companies to reassure investors that their millions of dollars are now in ‘clinical trials’. What is more, retrospective analyses of the hundreds of patients xenotransplanted in earlier trials are not yet complete.

The big risk is that although some countries can be expected to enforce stringent controls, the same is not true of all. Once trials become routine they will inexorably result in riskier trials being pursued somewhere using, for example, virus-laden baboons. Public concerns over the risks of xenotransplantation have already obliged the United States to take its scandalously lax original 1996 guidelines back to the drawing board. A wide public and political debate followed by an international agreement must be in place before pigs or any other animals are allowed into the clinic. Meanwhile, the progress in growing human embryo stem cells (see above) may yet yield a better alternative.