Who owns stem cells? And more to the point, who should own the life-altering medical treatments that may one day emerge from this futuristic and highly contentious field of research?

It may seem premature to worry about ownership rights for technologies that do not yet exist--and may never prove commercially viable. But with more money pouring into embryonic stem cell research--especially after the success of a ballot initiative in California last year, mandating $3bn in state funding for embryonic stem cells--disputes over ownership rights cannot be far behind, legal experts say.

Stem cell research has been a focus for intense political and ethical battles for years. Now the next frontier is in the courts: battles over who owns what in a field where intellectual-property rights are far from clear.

"Typically litigation only arises when there are commercially available products and a very real market for the technology", notes Bill Warren, an expert on biotechnology patents at the law firm Sutherland Asbill & Brennan in Atlanta. But now that California and other states are getting into the game of financing stem cell research, that will hasten the development of the technology, says Warren, and "litigation will definitely be coming", possibly in the next five years.

Up to now, legal experts point out, there has been very little US litigation involving stem cells, even though one organisation claims to own the patent rights to all embryonic stem cells. That group, the Wisconsin Alumni Research Foundation (WARF), says its patents cover "a method of culturing human embryonic stem cells and composition of matter which covers any cells with the characteristics of stem cells"--in other words, pretty much anything to do with embryonic stem cell research.

Critics, in the academic and commercial research communities, complain that this patent is too broad. But WARF and the US Patent and Trademark Office defend it, on the grounds that if others believe they have rival rights, they can fight it out in court.

There has been very little US litigation over stem cells. The truce may not last.

And despite the breadth of its patents, WARF is so far not impeding anyone else's research activities, says Arti Rai, an expert on scientific patents at Duke University Law School, pointing out that WARF freely licenses its patent for research purposes. But the current truce may not last long, she states, once WARF's rivals in the field are ready to commercialise their own technology. At that point, the breadth and validity of WARF's patents will be challenged in court.

Critics who see stem cell patents as an impediment to the development of lifesaving technologies are just plain wrong, says Michael Werner, chief of policy at BIO, the Biotechnology Industry Organisation. "Intellectual property is critical to scientific advancement", he observes. "There would be no private investment without patent rights". The only thing that will stifle stem cell research, he adds, is threatening the IP rights of those who carry it out for profit.

He places the debate over stem cell patents squarely at the centre of a larger social debate--in the US and elsewhere--over how to balance the intellectual-property protection needed to convince companies to invest in innovation with the need to maintain the kind of vibrant public domain that also is capable of fostering progress.

Everybody knows somebody who could one day be helped by a medical treatment based on stem cell technology. But the legal questions surrounding this promising technology are almost all as yet unresolved. And the issue of who owns the results of stem cell research can only get more complicated, as more and more American states start their own programmes to fund stem cell experimentation, creating a tangled web of private and public financing that can only, in the end, be resolved by the courts.