SPERM banks are big business in the United States and donors overwhelmingly seek anonymity. But sperm-donor offspring increasingly want to meet their biological fathers. David Crary reports.

Katrina Clark and Lindsay Greenawalt have much in common. Bright women in their 20s, raised by single mothers, keenly curious about the men whose donated sperm helped give them life.

Clark's search for her father succeeded after only a month, though with a bittersweet aftermath. Greenawalt is still searching, seven years after she started - persisting despite doubts and frustrations.

"I've dreamt of you since I was a little girl," Greenawalt wrote to her unknown dad in a Father's Day blog in June. "There are so many things I want to know about you."

Greenawalt, who lives near Cleveland, Ohio, the US, and Clark, a college student in Washington, DC, are part of an increasingly outspoken generation of donor offspring. They want to transform the dynamics of sperm donation so children's interests have more weight and it's easier to learn about their biological fathers.

One specific goal - a ban on anonymous sperm donations - seems far off in the US, although Britain and several other European countries have already taken that step.

But the voices of donor offspring are being heard more widely and clearly than ever, thanks to Internet-based social networking and other recent developments.

A new film, "The Kids Are All Right," depicts two teenage siblings who track down their sperm-donor father and introduce him to their lesbian moms. Complications ensue, but the teens' yearning to meet their dad is portrayed empathetically.

The film opened weeks after the release of a provocative study by the Commission on Parenthood's Future, titled "My Daddy's Name is Donor." It surveyed 485 donor offspring, concluded they were more troubled and depression-prone than other young adults, and recommended ending anonymous sperm donation.

The study's authors said they sought to ignite a debate, and they succeeded - reaction included swirls of pro-and-con blogosphere commentary and op-eds in several major newspapers.

"The adult voices of donor offspring are a welcome counterbalance to an array of cultural forces aimed at further marginalizing fathers," wrote Washington Post columnist Kathleen Parker. "At the very least, as this study implores, it is time for a serious debate on the ethics, meaning and practice of donor conception."

An increasing number of US sperm banks now offer identity-release policies, in which donors agree to let their offspring contact the donor when they turn 18. But many donors still opt for anonymity, producing the kind of frustrations encountered by Lindsay Greenawalt.

A Kent State University graduate who aspires to be a medical librarian, Greenawalt has been searching since 2003 for the biological dad she knows only as "Xytex donor 2035" - the number assigned to him in the 1980s by the Xytex Corp sperm bank in Augusta, Georgia.

She knows the man is now 49, attended college, and - like Lindsay - has brown hair and greenish eyes. She also knows a few medical details, thanks to an update the man recently sent to Xytex after Greenawalt requested it.

But learning of the medical update saddened Greenawalt, because no note came with it.

"He knows I'm looking for him - and he doesn't want to make contact," Greenawalt said, conceding that this gave her doubts about what she'd do if she did manage to identify him.

Her lengthy search has taken a toll in other ways.

"It's been a very sore topic with my mom - she felt it was a personal attack against her, that she hadn't been a good parent," Greenawalt said. "It's none of that. It's something we've got to do that's separate from how we were raised."

Since 2008, Greenawalt, 25, has been chronicling her quest on a blog, "Confessions of a Cryokid." A wrenching tale came last Thanksgiving, when she addressed the oft-repeated refrain that donor-conceived children ought to be grateful they were born.

"If I had to choose between being conceived with half of my identity and half of my kinship deliberately denied from me for eternity - or never being born - I'd choose never being born," she wrote. "We were created to carry a loss. A loss that no human being should have to endure."

The plight of donor offspring like Greenawalt deeply touches Katrina Clark, who surprised herself in 2006 by discovering the identity of her father on the Internet after a few weeks' research. She sent him an e-mail and got a prompt, friendly reply, with a photograph included.

Since then, however, "our communication has been pretty much nonexistent" and they have not met face-to-face, said Clark, a 21-year-old student at Gallaudet University who is frustrated by the impasse.

"Maybe I pushed or pulled too much," Clark said. "He wasn't ready to be out in the open. Perhaps he was embarrassed or ashamed.

"I still wonder about him," she added. "There's so much about him I still don't know."

At one point, Clark soured on the entire idea of donor conception. Now she accepts that it can be a blessing for some families, but she favors ending donor anonymity and hopes more parents will tell the truth early on to their donor-conceived children.

"The most damaging thing I've seen is when parents wait to tell," she said.

In an article she wrote for The Washington Post in 2006, Clark described the emotions that wracked her as an adolescent.

"I realized that I am, in a sense, a freak," she wrote. "I finally understood what it meant to be donor-conceived, and I hated it."

She evolved into a dedicated activist, even lobbying for an unsuccessful bill that would have made Virginia the first state to ban anonymous sperm donations.

The American Society for Reproductive Medicine, which represents many sperm banks and fertility clinics, encourages parents of donor-conceived offspring to tell their children the truth about their conception.

But it does not favor banning anonymous donations, saying children's rights must be balanced against the interests of donors and parents who will raise the child.

Dr Jamie Grifo of New York University's Fertility Center, said heavy emphasis on the rights of a child wouldn't always work in the realm of donor-assisted conception.

"It may not be a popular point of view, but when these decisions are made by donor and a parent, the child doesn't have a say," he said. "If the contract is for it to be anonymous, it should remain anonymous, and the child just has to deal with that."