They are surviving members of what Irene Hizme calls "the most exclusive club in the world": Jewish twins hand-picked by the Nazi physician Josef Mengele at the Auschwitz-Birkenau death camp to be guinea pigs, in her words, "for experimentation to develop a master race."
Irene Hizme was 6 years old at the time. For years afterward, she thought she would carry her awful secret to the grave. "To talk about it," she said last week, "is a descent into darkness."
Eva Kor of Terre Haute, Ind., could not bring herself to describe the scenes of horror to her children. "The pain was too great," she said.
Peter Somogyi, a New Jersey businessman, said he has put the nightmare behind him. But his wife says his cries of torment still awaken him in a cold sweat.
Nearly a half-century after they entered the gates of Auschwitz, the twins are being heard as never before.
"Children of the Flames," a book by Lucette Matalon Lagnado and Sheila Cohn Dekel to be released today by William Morrow, describes the blighted histories of twins who have come forward in recent years.
Some, like Mrs. Hizme, who lives in Oceanside, N.Y., are forcing themselves to speak in public for the first time.
Mengele selected about 1,500 sets of twins -- Jews, Gypsies and others -- for projects conducted at his genetics laboratory. Many died in the research; at the end of the war, fewer than 200 individuals were alive.
In the experiments, many had blood drained and transfused in research that was said to be connected with Mengele's hunt for ways to increase the fertility and birthrates of German women. He also tried to find ways to change eye color.
Mengele worked on one twin and used the other for comparison.
Twenty-seven known survivors of the experiments live in the United States, most of them in the New York metropolitan area. Six are in Canada, and about 100 live in Israel and elsewhere.
Some survivors say they believe there are others still alive who have allowed their past to remain locked in secrecy, too anguished by the experiments performed on them to speak out.
Some, who were toddlers when Mengele and his staff subjected them to radical tests and surgical procedures, might have camp tattoos and unexplained scars but no conscious memory of the ordeal.
Little evidence of the research exists. It is thought that, after the war, Mengele either destroyed his records and tissue samples or carried them into hiding, first in Europe and then in South America.
In more than 40 years, Mengele's death has been reported many times. In 1985, his son and some experts identified the remains of a man who drowned in 1979 as his.
"On the surface, we enjoy normal lives, but we have never escaped the long, dark shadow of Mengele," said Mrs. Hizme, a 53-year-old mother of two. "If I push it out of my day, it returns at night."
Mrs. Hizme was speaking before a hushed audience at Congregation Ohab Zedek in Manhattan at an observance of Holocaust Memorial Week last Wednesday.
The memory that never ages haunts the survivors even as they grow old. In recent interviews, they said they carried a burden that other survivors of the camps do not: that their selection for Mengele's experiments spared their lives.
Their families died at Auschwitz. So did children who were not selected for the research.
"If childhood is the foundation of a human being's life," said Mrs. Kor, who was 9 when she arrived at Auschwitz in 1944, "then what kind of foundation can we have if our memories are filled with the smell of burning flesh and chimneys belching the black smoke of our families?"
There was one other difference, and for the twins it is the hardest to explain.
Mengele, known as the "Angel of Death" for his role in choosing who would live and who would die, was also, for them, Mengele the protector.
As long as he required them for his research, they were spared.
Giving blood samples and submitting to X-rays and injections were daily options to death, even though most of the twins would eventually die painful deaths, as did those who entered the crematorium on their first day in Auschwitz.
Even the young ones, like Irene Hizme, understood the deadly game. Her parents had taken their children and fled from their native Germany to Czechoslovakia to escape Hitler, but all were rounded up in 1943 and transported to Auschwitz.
Given special status, the twins lived in their own barracks, separated by sex. They got an extra ration of food once or twice a week and were given the medical care denied to tens of thousands of others.
"Savior and demon," was the way Mrs. Hizme described the children's ambivalent view of Mengele. Even today, survivors describe him as kindly and avuncular. They say he gave them candy and kissed them.