About 400,000 human embryos are kept in frozen storage in the United States, with little agreement on what to do with the thousands that are unclaimed.

Donate them for research? Give them to infertile couples? Keep them in storage indefinitely?

Fertility specialist Dr. Michael Feinman sees them as potential life. "It's unconscionable to have freezers with unclaimed embryos," he said.

Nationally, the closest thing to a count of unclaimed embryos is about 16,000 - a figure that came out of a 2002 study for the Society for Assisted Reproductive Technology, a Washington, D.C., agency that oversees about 94 percent of fertility clinics. The study, called "Cryopreserved Embryos in the United States and Their Availability for Research," suggests that up to 4 percent of the nation's frozen embryos are unclaimed.

Feinman, with 10 percent unclaimed just in his California office, said he believes the national number might be higher. "Nobody really knows how many unclaimed embryos there are, but they're in the hundreds of thousands," he said.

An "unclaimed" embryo is one whose donors haven't renewed their storage contract or responded to repeated correspondence from the storage facility.

In his office, Feinman unscrewed a sealed lid on a cryogenic tank as a cloud of liquid nitrogen billowed out. He reached into the cream-colored metal can - which was just a bit larger than an old-fashioned milk can - to reveal a smaller metal can inside. Around the periphery of the smaller can are dozens of straws no larger than coffee stirrers. Each straw contains five or six frozen embryos, which are smaller than the tip of a needle.

A frozen embryo is essentially a human egg that has been fertilized by sperm in a petri dish, and then frozen. Research is being conducted right now on methods to successfully freeze unfertilized eggs, but to date, unfertilized eggs are considered too fragile to freeze for use in pregnancy later.

One Los Angeles cryogenic storage facility, California Cryobank, reports 100 to 200 of its embryos are unclaimed, although it doesn't keep track of the total number of embryos. It counts clients - also 100 to 200 - each of whom stores anywhere from one to dozens of embryos.

"This is the elephant in the room. Every doctor is stressed about embryo storage growing bigger and bigger and bigger," said JoAnn Eiman, founder of Snowflake Frozen Embryo Adoption, a California adoption agency for leftover frozen embryos.

The reasons people neglect their frozen embryos vary. Sometimes people simply forget about them, Feinman said.

"A couple comes in from out of town, does an egg retrieval, gets pregnant with twins and they're busy off with their twins and their lives or they move and you lose track of them," Feinman said.

Randy and Tammy Smith say they didn't understand they would be responsible for frozen fertilized eggs left over from their in vitro procedure. The Smiths, checking on a lark on what they thought were unfertilized eggs in storage, discovered they had leftover embryos in storage since 1990.

Tammy Smith, a 39-year-old kindergarten teacher and already a mother of four, had heard a radio program about donating eggs. It made her curious about whether she had eggs left over from her in vitro fertilization procedure at Cedars-Sinai Medical Center in Los Angeles.

Randy Smith, also a teacher, said he was stunned when his wife called to tell him they had 13 embryos, not eggs, sitting in a freezer.

Because they believe life begins at conception, the couple arranged to have all of the embryos thawed and the viable ones implanted. One attached to Tammy's uterus, and some national fertility experts believe her baby, Micah, who arrived Oct. 18, was born from what could be the oldest embryo ever used successfully.

"This isn't the first time I've seen cases like this where patients later discover that they have embryos that they never knew about," attorney Melanie Blum said. "I've seen this happen over and over and over again."

Shortly after the Smiths made their discovery, they contacted Blum, who specializes in reproductive law, to sue the doctor who fertilized the eggs. Blum filed the complaint, but a Santa Monica judge dismissed it.

Nobody is sure why the Smiths weren't notified about the frozen embryos. For 11 years, the Smiths said, nobody contacted them, billed them or even told them the embryos existed.

Dr. Mark Surrey, the in vitro specialist who mixed Micah's embryo in a petri dish 13 years ago, said that as far as he knows, his office did try to contact the Smiths and "completely documented it."

Surrey was working at Cedars-Sinai Medical Center in Los Angeles at the time.

Cedars-Sinai representative Sandy Van looked into it but got no results.

"It's so long ago, I wouldn't have anybody who would know," she said.

She noted Cedars' in vitro fertilization lab was destroyed in the 1994 Northridge earthquake, although she wasn't sure if that was a contributing factor.

Feinman, who performed the in vitro procedure that resulted in Micah's birth, would not be surprised if somebody lost track of the Smiths, who moved three times during the past 13 years. He pointed out that computer tracking was not nearly as sophisticated then.

"You lose track of them unless you have an automated system that sends out a letter that says, 'Don't forget you have frozen embryos and you owe us $500,' " Feinman said.