AUSTIN, Tex., Oct. 12 - The inmates at the Allred Unit, a tough Texas prison, mostly go by names like Monster, Diablo and Animal. They gave Roderick Johnson, a black gay man with a gentle manner, a different sort of name when he arrived there in September 2000. They called him Coco.

Under the protocols of the prison gangs at Allred, gay prisoners must take women's names. Then they are assigned to one of the gangs.

"The Crips already had a homosexual that was with them," Mr. Johnson explained. "The Gangster Disciples, from what I understand, hadn't had a homosexual under them in a while. So that's why I was automatically, like, given to them."

According to court papers and his own detailed account, the Gangster Disciples and then other gangs treated Mr. Johnson as a sex slave. They bought and sold him, and they rented him out. Some sex acts cost $5, others $10.

Last month, a federal appeals court allowed a civil rights lawsuit that Mr. Johnson has filed against prison officials to go to trial. The ruling, the first to acknowledge the equal protection rights of homosexuals abused in prison, said the evidence in the case was "horrific."

"I was forced into oral sex and anal sex on a daily basis," said Mr. Johnson, who has been living in a boarding house here since his release in December. "Not for a month or two. For, like, 18 months."

The phenomenon of sexual slavery in prison has only recently emerged from the shadows. Prison rape, in general, has received sporadic notice over the years and sustained attention more recently, with the passage last year of a federal law that aims to eliminate it. But there has never been a comprehensive study of incarcerated gay men subjected to sexual abuse.

Discussing any form of prison rape is difficult. It makes many people uncomfortable. Some find it amusing.

"It has been the subject of mockery and almost sadistic glee," said Margaret Winter, associate director of the National Prison Project of the American Civil Liberties Union. "But Roderick is a human being who doesn't deserve this, not in a civilized society."

The civil liberties union represents Mr. Johnson in his lawsuit, which will go to trial next summer.

Sipping a beer in the courtyard of a hotel this week, Mr. Johnson displayed the affable good nature of the restaurant manager and car salesman he used to be. He is a compact, trim man - 5 feet, 9 inches, 170 pounds - who dresses neatly, talks easily and has bright, expressive eyes.

"I'm the first person in my family to get a taste of prison," he said, with more than a little shame. His crimes were relatively minor and all nonviolent - burglary, a bad check, cocaine possession - but they were enough to send him to Allred, a maximum security prison 250 miles north of here, on the Oklahoma border. According to state prison records, Allred ranked second among the more than 70 Texas prisons in the number of sexual assaults in the two years ending in August 2003. It reported 50 out of 635, with the Telford unit in Bowie County first, with 59.

Mr. Johnson's suit says he begged prison officials to move him to a unit called safekeeping, where white and Hispanic homosexuals, former gang members and convicted police officers lived. He asked seven times, in writing.

The officials did nothing, saying Mr. Johnson's claims could not be corroborated. At prison hearings, Mr. Johnson said, officials would take pleasure in his plight. They suggested that he was enjoying the rapes, he said.

Mr. Johnson said they told him he had two choices. One was to fight. The other was to engage in sex. The officials deny they mishandled the complaints and the ugly comments attributed to them.

Carl Reynolds, the general counsel of the Texas Department of Criminal Justice, which runs the Texas prisons, said Mr. Johnson's complaints were properly handled.

"These allegations were investigated by the internal affairs branch of our agency," he said. "There seems to have been a lot of doubt about his motives and his ability to present evidence."

He added that the problem of prison rape was real and that Texas was committed to solving it. The new federal law, the Prison Rape Elimination Act, says that, by a conservative estimate, 13 percent of inmates in the United States are sexually assaulted in prison. The law calls for research into the problem by the Justice Department, which will recommend policy changes based on the studies.

A 2001 Human Rights Watch report on prison rape touched on the subject of sexual slavery.

"Six Texas inmates, separately and independently, gave Human Rights Watch firsthand accounts of being forced into this type of sexual slavery, having been 'sold' or 'rented' out to other inmates," the report said. Those inmates, and other Texas prisoners, told the group that sexual slavery "is commonplace in the system's most dangerous prison units." The group said it also "collected personal testimonies form inmates in Illinois, Michigan, California and Arkansas who have survived situations of sexual slavery."

State prison systems elsewhere in the country told Human Rights Watch that prison rapes were relatively rare. Colorado, Kansas, Kentucky, Missouri, New Jersey, Oregon, Pennsylvania, South Dakota and Wisconsin reported fewer than 10 cases annually. Arizona, New York and North Carolina reported 10 to 50.

Mr. Johnson filed his lawsuit in Federal District Court in Wichita Falls, Tex., in April 2002, seeking protection and monetary damages. His claims were spelled out in legal papers, 300 pages of sworn testimony and a series of interviews.

Early in Mr. Johnson's time at Allred, a member of the Gangster Disciples claimed Mr. Johnson as a sort of wife. The gang member forced Mr. Johnson to make his bed, clean his cell and cook food for him on a hot pot. He also forced Mr. Johnson to have sex with him.

Mr. Johnson was later sold to the Bloods and then to other gangs, he said. Once, a bidding war broke out. He was told he was worth $100 in the open market.

"They would prostitute you out, sell you for $5 or $10 of commissary," he said, referring to credit at the prison store. "Or cigarettes. Or cash money."

Once, Mr. Johnson was raped by eight men, one after the other, he said in the suit. He was raped in cells and stairwells, he said, but the showers were the worst. "It's like throwing a piece of meat to a pack of wolves," he said.

Throughout, he was called Coco. The other prisoners used feminine pronouns - she, her - when they talked about him. "If you are homosexual," Mr. Johnson said, "you are considered a female among these men and you will take on the name of a female. You do not go by the name Roderick because that's considered disrespecting any man that's on the facility."

Gang members humiliated Mr. Johnson and other inmates for sport, in scenes reminiscent of the abuse at the Abu Ghraib prison in Iraq.

On March 17, 2002, according to Mr. Johnson's court filings, members of a gang called the Mexican Mafia forced him and a mentally ill man known as Alazar to masturbate each other in the shower. They repeatedly forced Alazar to insert his finger into Mr. Johnson's anus and then to lick his own finger.

Thinking back on his ordeal in prison, Mr. Johnson said: "It broke my spirit. It broke my pride."

He grew up in a large farming family in Marshall, in northeast Texas. His cousin, Sharon Bailey, recalled, "We all went to church together, with my mother driving me, Roderick and his sister to Sunday school each week."

He joined the Navy at 17, visiting Thailand, Singapore and Japan on the U.S.S. Alamo. His troubles started after he was discharged, he said, when he burglarized a neighbor's house in Marshall in 1992. He had fallen under the sway of a boyfriend who ran with a bad crowd, he said.

The crime earned him a 90-day sentence and 10 years of probation. After serving his sentence, he went on to hold a series of decent jobs, but drug use and the resulting probation violations put him back in prison.

A Texas prison, he said, is no place for a gay man.

"You've got rednecks here in Texas who run these prison systems," Mr. Johnson said. "A black man suffering, especially a gay black man suffering, is right up their alley."

At a deposition in 2002, a lawyer for the prison officials, Deven Desai, questioned Mr. Johnson's religious faith, an issue with no obvious connection to legal claims in the suit.

"How do you as a Christian man balance your homosexuality with your Christianity?" Mr. Desai asked.

"I really don't feel that I'm any different from anyone else who serves God," Mr. Johnson answered.

The doctors say he has post-traumatic stress disorder, and he receives disability payments from Social Security. He shares a room in a private boarding house for former prisoners, hard by the highway.

He takes antidepressants and goes to counseling to get through the days. The nights, he said, are harder. "I'm trying to keep my sanity," he said.