Hats off to Harvard and the University of California at San Francisco for undertaking stem cell research that the Bush administration is trying to discourage and political leaders in Washington seem unwilling to support. Both institutions have started programs to clone human embryos and extract stem cells from them, thus creating stem cell lines tailor-made to study specific diseases. Their bold moves, made after intense soul-searching over the ethical and scientific issues, should help to revive a promising field of research — known as therapeutic or research cloning — that had been staggered by a scandal in South Korea.

Under current Bush administration policy, scientists who rely on federal money can use only a limited number of stem cell lines derived from surplus embryos at fertility clinics. The only serious political debate in Washington is whether to use a larger array of surplus embryos from fertility clinics. But such lines are unsuitable for the most important research because they can seldom be linked to specific diseases.

Now the Harvard and California scientists, using only private funds, plan to develop stem cell lines that will be genetically matched to patients with diseases like diabetes, Parkinson’s, Lou Gehrig’s disease, and certain blood disorders. The scientists will take the nucleus of a cell from a diseased patient and inject it into an egg whose own nucleus has been removed. They will then stimulate the egg to produce an embryo, genetically matched to the patient, from which stem cells can be extracted. The goal is to study how these diseases develop and, ultimately, find ways to treat them with replacement cells that would not be rejected by a patient’s immune system.

The task won’t be easy. No one has yet created a cloned human embryo and extracted stem cells from it. A Korean team that claimed to have achieved the feat was found to have fabricated its results, so the whole field was pushed back to the starting line, in a sense. There may also be practical problems in obtaining enough human eggs for the experiments. And any clinical applications may be a decade or more away. But the potential is enormous, and it is fortunate that these two institutions, and a handful of other laboratories around the world, are getting started.