U.S. biotechnology firms specializing in stem-cell research gave back their gains on Friday after President Bush's announcement that the federal government would provide funding for limited stem-cell research didn't go as far as some had wished.

The Republican president said he would allow the federal government to finance research only on some 60 stem-cell lines worldwide whose embryos have already been destroyed, meaning there is no chance of life emerging from them.

The stocks jumped on Thursday amid optimism the president would allow federal funding for at least some aspects of the science that deals with parent cells whose progeny can be coaxed to evolve into any of more than 200 different cell types in the body.

But biotech analysts and fund managers called the roller coaster ride for stocks like Geron Corp. and StemCells Inc. irrational speculation, saying stem-cell research is too far away from developing commercial technology and therapies to make sensible bets.

``The recent moves of these stocks on the back of this decision are not justified because this decision does not in any way improve the fate of these companies and whether they will be able to bring anything to market soon,'' said Michael Sjostrom, chief investment officer of Sectoral Asset Management and manager of the Pictet Biotech Fund that has assets of $1.5 billion.

``The potential in stem-cell research is important when you think about what it can do, but it is very long term,'' he said.

Shares of Stemcells, a Palo Alto, California-based company that aims to create cell-based treatments of diseases of the central nervous system, liver and pancreas, fell 20.2 percent, or $1.30, to $5.15.

Menlo Park, California-based Geron, a stem-cell research firm targeting therapies for cancer and promotes tissue repair in chronic degenerative diseases, saw its shares fall 7.4 percent, or $1.11, to $13.83.

Aastrom Biosciences Inc. saw its shares tumble 16.4 percent, or 37 cents, to $1.88. The Ann Arbor, Michigan-based cell research company has developed equipment used to incubate different types of human cells, including stem cells, in order to increase their numbers.

On the up side, Australian biotech firm BresaGen Ltd., which said it holds four of the 60 existing embryo stem cell lines Bush said could receive federal funding, saw its shares climb 13.3 percent on Friday to close up 11 cents at 94 cents.

BresaGen is using its cell lines as part of research into Parkinson's disease at its program in Athens, Georgia.

``It's far too unclear who the leaders are going to be in terms of commercial development, so as an investor, it's hard to look at these companies involved with this too seriously because there are too many uncertainties,'' said Brian Sheehy of Brinson Partners, a unit of UBS Asset Management.