In October, Laura Ross-Adams received an odd e-mail from a woman in Oregon.

The writer, a nurse-midwife named Chris Beard, explained that she had recently adopted a little girl from China, and she had come to believe her daughter could be one of a pair of twins.

Beard said she had checked the directory of an Internet adoption site, and saw that her daughter, Ruby, and Ross-Adams's daughter, Sarah, shared not only their birthday but their former residence -- the First Social Welfare Institute of Changsha, in Hunan province.

It might sound a little kooky, Beard wrote, but would Ross-Adams be willing to look at photographs of Ruby and see whether the girls bore any resemblance?

Ross-Adams, an orthopedic surgeon who lives in Medford, N.J., was skeptical: What were the odds of these girls being related? Maybe a million to one.

Still, she agreed to look at the photos. The next day, in shock, she wrote back: "We have twin daughters."

"There was one picture that was so striking, I thought she had somehow gotten pictures of Sarah," Ross-Adams says.

Phone calls followed, and more pictures traded. Both families, grounded in medicine, wanted hard evidence to confirm or refute their belief.

They decided to pursue DNA tests, knowing the science can be limited in its ability to connect siblings, not always delivering the yes-or-no answer it routinely provides on television crime shows.

The test results: A 93 percent likelihood that the girls shared at least one biological parent.

With that, Ruby and Sarah, both 3, both with the same thick eyebrows and the same dimpled cheek, had found the one thing Chinese adoptees were never supposed to be able to find: a blood relative. And two more families had unexpectedly become part of a phenomenon that is turning the adoptive community on its ear.

DNA testing has been used to identify the bones of kings and outlaws, to put people in prison and get them out, to give name to the fragmentary remains of soldiers lost on distant battlefields. Now it's being put to a new task: to locate biological siblings among the thousands of Chinese girls adopted into homes here during the last decade.

So far, about half a dozen pairs of sisters have been publicly identified. But because some families keep their discoveries private, a Houston geneticist believes that the true number could be as high as 40. And a Web site called Sister Far, which limits registration to parents who have found or think they've found a sibling, has grown to 110 members.

For an entire community, the impossible has become possible. And that new reality is sparking new controversy, forcing adoptive parents to confront questions that strike at the heart of how their families are formed and who they perceive themselves to be.

Does the right to search -- and to test -- belong to the parent or the child? What evidence, if any, should be grounds for initiating a search? And if the bonds of adoptive families are as real and permanent as those of biological families -- and adoptive parents insist that they are -- is it hypocritical to look for a blood relation?

"It's so emotionally loaded," says Karin Evans, author of "The Lost Daughters of China: Abandoned Girls, Their Journey to America, and the Search for a Missing Past."

Some parents believe that they face a damnable choice: If they search, will their child think that the adoptive tie is being undercut? If they don't, will their child blame them later for not seeking out facts when they might have been found?

In the absence of any guidelines, hundreds of parents are forging ahead.

Two dozen Web sites have sprung up with names such as Hunan Sibling Find and Jiangxi Sibling Find, places where parents can post photos of their children and sift through pictures of others, searching for a resemblance. One adoptee DNA data bank is already up and operating -- Kinsearch Registry of Atlanta -- and a group of parents has formed the a-China DNA Project to start another.

"We know these kids have siblings out there," says Mary Coolbaugh-Murphy, a project founder and a geneticist at the University of Texas's M.D. Anderson Cancer Center who has two Chinese daughters. "But you're not going to find them by a photo registry because siblings don't always look alike. The way to do it is DNA matching."

In 1998, China scholar Kay Johnson showed that many adoptees probably had sisters and brothers living in China. But hardly anyone thought they could have siblings here.

The reasons are as intricate and complex as the culture that defines Chinese society, and as simple and logical as a child's set of toy stacking cups, one fitting neatly into the next.

Start with this: Nearly all the adoptees are girls, abandoned by Chinese parents barred from having more than one child and pressured by societal mores to raise sons. Because China's population-control laws make it illegal to have "extra" children -- and to surrender children for adoption -- the girls are forsaken in secret, dropped off in bus depots and railway stations.

Yet only a fraction of Chinese parents ever abandon a child. And even fewer give up two.

Most of those girls are informally adopted, taken in by childless couples or by parents who want a daughter and a son. Some are claimed by strangers, plucked from park benches and city hall gates. Others die of illness or exposure.

So only a percentage of children who are abandoned enter the state welfare system. There, the numbers are thinned again.

Only some orphanages participate in international adoption programs. Among those, only a small percentage of children find new homes. Of those children, only some go to the same country.

Because it seemed impossible that two related children could travel that route, included at every junction within a fraction of a fraction of a fraction, the first DNA matches were regarded as flukes.

"Yes, it's a billion-to-one thing," says Bonnie Ward, a Liberty Mutual executive in New Hampshire, who discovered that the daughters she adopted three years apart were biological sisters. "But it's possible."

How? Nobody knows. Not for sure. Johnson offers a theory that could shortcut the chain of unlikelihoods: If Chinese parents who abandon a second child were to leave that baby at the same spot where they left her sibling, that could increase the odds of both entering the same institution.

So far, the discoveries in this country have tended to follow similar paths of luck, intuition and inquiry: A chance meeting or e-mail between parents. The realization that their girls came from the same orphanage -- and that they share certain traits. An exchange of photos showing an uncanny resemblance, followed by DNA tests.

A key factor in these identifications, experts say, is that the size of the community has reached critical mass. Today, the United States is home to nearly 50,000 Chinese adoptees, and that figure is growing at a rate of 7,000 a year. Many families belong to a nationwide support organization, Families With Children From China, a powerful tool for spreading information.

Second, parents who want to search are benefiting from a convergence of technologies, all improved since the first girls came here in the 1990s. The Internet, once a strange new device, is now used by 55 percent of Americans, according to census statistics. Genetic testing has become more sophisticated -- and accessible. Today, anyone with a credit card can obtain a test kit through the mail.

Fees are dropping, too. For instance, it costs $250 to register a DNA sample with Kinsearch.

"If there's any way of finding a sibling," says Kinsearch Executive Director Barbara Rappaport, "it would be wonderful."

When they met for the first time Sarah Adams and Ruby Beard momentarily hung back, hiding behind the legs of the grown-ups.

They were introduced on a rainy Friday night in June, in a hotel room at the Flying W Airport Resort in South Jersey. Within five minutes, they were laughing and wrestling on the bed, leaving their parents to watch and wonder.

The girls have the same voice. Same laugh. Same posture. There are differences, too. Ruby is heavier, Sarah taller. In some photos, they look identical, but in others, nothing alike.

Ross-Adams and her husband, David, plan to take Sarah to Oregon in the spring. Both families wonder what the future will bring, how they and their children will manage this new relationship.

"We didn't choose each other, but we have a link," Beard says. "I want to forge the bonds."

In adopting from China, Ross-Adams says, she knew she would face her daughter's inevitable questions: Why don't I look like you? What happened to my Chinese mommy?

Now she foresees others: Why doesn't my sister live with me? Why can't we be together?

"What's going to happen as she gets older?" Ross-Adams says. "I think a lot about that."

Sarah Adams, 3, with dad David and mom Laura, above; and Ruby Beard, also 3, with mom Christine, below. DNA tests determined that there was a 93 percent likelihood that Sarah and Ruby, adopted separately from China, shared at least one biological parent.