Sixty-four human embryonic stem cell colonies that officials say can be used for federally funded studies are enough to keep scientists busy for years doing basic research, some experts say.

The National Institutes of Health on Monday identified 10 labs that have developed 64 embryonic stem cell lines that are approved for use in government research.

The action silenced weeks of skepticism during which some experts questioned whether the cell lines existed. Nonetheless, some experts said again Monday that the 64 lines may not be adequate.

However, Health and Human Services Secretary Tommy Thompson said it was time for researchers to get to work.

"The scientific community must seize the moment," Thompson said following the NIH announcement.

Monday's announcement was the next step in a process that started earlier this month when President Bush said his administration would fund embryonic stem cell studies, but only for cell lines developed before Aug. 9.

Embryonic stem cell studies are opposed by some church groups and by some in Congress because to make the cell colonies requires the death of a human embryo, an act some consider to be homicide. Bush's decision permits federal research, but only on cells coming from embryos processed before the cutoff date. He also required that the cells be derived from embryos considered surplus at fertility clinics and which were donated for research, without compensation, by couples who were fully informed about the process.

NIH said the eligible cell lines were developed at four U.S. labs, at two labs each in India and Sweden and at one lab each in Australia and Israel. Goteborg University in Sweden had the most lines with a total of 19, NIH said.

At CyThera Inc. of San Diego, which NIH said has nine cell colonies, company officials said their first cell line would be ready for use by other researchers sometime next year.

Michael J. Ross, the CyThera chief executive, deflected criticism that the 64 cell lines may not be enough to harvest the full medical benefits of stem cells.

"This is a very good start," said Ross, noting that government funding of the research is an "evolving process" and that more cell lines may be available later. He said scientists can spend years on the 64 available cell lines.

"Many scientific questions can be answered under the rules set up by President Bush," said Lutz Giebel, CyThera's chief scientist.

W. Sue Shafer, assistant vice chancellor at the University of California, San Francisco, said her institution's two cell lines would be available to researchers "within a few months." First, she said, the university must develop a material transfer agreement and work out such details as to what to charge to recover the costs of making and shipping the cells.

"We're eager to make them available to other people," she said.

Fifty research applications already have been filed to conduct research with six cell lines at Monash Institute of Reproduction and Development in Australia.

"We have already executed about a dozen agreements and we expect that applications will now increase," said Martin Pera of Monash. "With the opening up of NIH funding we can now collaborate with groups in the U.S. It's going to be very positive for the field as a whole."

BresaGen Inc., an Australia-based company with labs in Athens, Ga., has four cell lines on the NIH list, but company officials said that guidelines have not been drawn up to give access to outside researchers.

Meera Verma, general manager of Bresagen, said his company's stem cell lines were announced only in July, just weeks before Bush's deadline.

The Wisconsin Alumni Research Foundation, which holds the patent for five cell lines, along with a patent on a method for extracting and culturing stem cells, said it already has provided colonies of cells to about 30 researchers.

"We have enough cells from one line to fulfill (the) need of as many as could possibly get federal funding," said Andrew Cohn, a foundation spokesman.

But other experts continue to say that good science requires more than 64 cell lines.

Kevin Wilson, director of public policy at the American Society for Cell Biology, said many researchers believe "there is a question about the quality of the cell lines and if they are of sufficient genetic diversity for scientists to do the work that needs to be done."

Tony Mazzaschi, a research policy expert at the Association of American Medical Colleges, said there is concern that cell lines that work in one lab could not be nurtured in another -- a common experience in complex biological research. Should many cell lines prove unreliable in other labs, he said, "it could be a major stop sign" for the research.

Embryonic stem cells are the basic building blocks for the 260 or so cell types in the body. During development, stem cells transform into heart, muscle, brain, skin or other tissue.

Researchers hope that by guiding this transformation, they can coax stem cells to make new cells that could be used to treat diabetes, Parkinson's, heart disease or other disorders.

The five Wisconsin Alumni Research Foundation cell lines were developed by Dr. James Thomson, a University of Wisconsin researcher who in 1998 became the first to isolate and patent human embryonic stem cells. The patent was transferred to WARF, which now controls the cells.

WARF charges $5,000 for two vials, each containing about 1 million stem cells. Ross said this is a modest "break-even" charge and he expects CyThera to follow a similar system.

"We're not going to be selling them to make money," but will recover the cost, said Shafer of UCSF.

Cohn said earlier that WARF claims a patent interest in any human stem cell line developed with techniques pioneered by Thomson. Just how many of the 64 lines would be affected was not immediately known, but CyThera officials said they did not use the Thomson system and were, in fact, applying for a competing patent.