The question of when a formless clump of developing cells can truly be said to become a human will never have a clear answer. It depends on whom you ask: biologists, theologians, and pro-life and pro-choice campaigners have all wrestled with the concept for years. Regulations that cover the relevant scientific fields and issues should take all these conflicting views into account. Not everybody will be happy with the outcome, but, by definition, not everybody can be.

In October, the European Court of Justice (ECJ) took on the question. And rather than tip-toeing around the sensitivities, the judges of the court — the highest in Europe — trampled right through them. The ECJ had been asked by the German Supreme Court to clarify ambiguous wording in the European Union (EU) directive on the Legal Protection of Biotechnological Inventions, which bans patents on procedures that use human embryos. The ECJ responded with a clumsy ruling that outlaws patents involving stem cells derived from such embryos and, some critics say, raises questions about future research into regenerative medicine (see page 310). In doing so, the court effectively stepped over the line that separates the interpretation of law, which is its responsibility, from the creation of law, which is the job of parliaments and governments.

The ruling left many scientists, judges and legal experts in EU member states fuming.

For the most part, the ECJ does a faultless job. This time, however, it exceeded its competence. In the case under consideration, Greenpeace had claimed that the existing directive should outlaw a patent relying on human embryonic stem cells that had been taken out by Oliver Brüstle, director of the Institute of Reconstructive Neurobiology in Bonn, Germany. But are human embryonic stem cells equivalent to human embryos in this context? The German Supreme Court, which was handling the Greenpeace complaint, passed the question up to the ECJ.

Unfortunately, the ECJ chose not to confine its analysis to the patent context, but took it upon itself to define the term 'human embryo' generally (and in the broadest possible way), and to assess the surrounding moral environment. A human embryo, it said, comprises an ovum activated to divide by fertilization or any artificial means. Moreover, it added, any research involving human embryonic stem-cell lines is immoral, because such cell lines are originally derived from fertilized eggs.

The ruling left many scientists, judges and legal experts in Germany and other EU member states fuming. Not only because the court had issued a de facto legal definition of a human embryo, but because it had done so with shoddy reasoning and without appropriate legal references. In the case of ambiguous law, a court should go back and ponder the intention of the law-makers. From its brief justification in Brüstle v. Greenpeace, the ECJ seems not to have done that.

The ECJ is made up of judges from each EU member state, and critics argue that it simply does not have the technical expertise to deal with issues such as patenting, or stem cells. Yet the court is not held to account by any external watchdog, and its decisions cannot be appealed.

Last week, an alliance of ten major German research organizations, including the German Research Foundation (DFG, the country's national granting agency), the University Rectors Conference and the Max Planck Society, put out a statement condemning the decision. But the damage has been done. Battle lines have already been drawn in the European Parliament, with those opposed to research with human embryonic stem cells calling for funds to be frozen.

The only obvious route out of the confusion created by the ECJ is for the real law-makers — the European Parliament and the Council of the European Union — to amend the ambiguous EU directive that caused all the trouble. They should tighten its loose language on the legal definition of a human embryo in terms of patenting, so that the law reflects what the lawmakers originally intended. This will take courage (and time — the original directive was a decade in the works) but, as the ECJ ruling shows, for all its sensitivities, this is not a subject on which it pays to be vague.