All she wants is an audience with a court officer, she says, her voice echoing down the building's empty hallways. All she has are two questions: Why was her son put to death? What happened to his body?
The answer to the first question is in the charge sheet: He knifed a man to death in a brawl. The second answer, she is convinced, lies in a much-criticized Chinese practice - taking organs taken from executed prisoners for transplant surgery.
"Let me talk to someone! Give me justice!" Meng shouts as the guard blocks her way.
Ever since her son was convicted and executed in January 2005, Meng has been searching for an explanation. She never saw his body. His corpse, tagged No. 207, was put in a hospital van and taken to a crematorium.
By then, Meng believes, the body had been stripped of its organs.
"It would be unbelievably cruel to take his organs. It's the final insult," Meng says later, riding a public bus to yet another government office, lines of fatigue etched around her eyes.
She has no direct evidence to back up her belief, but the secrecy in which China has shrouded the whole issue has long bred suspicions, with foreign medical and human rights groups saying it is opaque, profit-driven, and indifferent to medical ethics.
What's new is that these critics are being joined by ordinary Chinese such as Meng, a 53-year-old apple farmer from the fringe of the Gobi Desert.
Over more than two years, Meng has made a dozen trips to this city in north-central China, borrowing money for the 46-hour train trip from the family farm. She has journeyed even farther, to Beijing, seeking central government intervention.
Each time she has been shunted among government agencies. In March, she said, officials in her hometown of Kuitun prevented her from leaving. "Ordinary people like us are like ants. The system just steps on them and destroys them," says Meng.
Much of the furor surrounds the use of organs - mostly kidneys, livers and corneas - from executed prisoners who may not have given their permission. Critics argue that death-row prisoners are not truly free to consent and may feel compelled to become donors, violating personal, religious or cultural beliefs.
In the United States, federal prisons ban inmates from donating organs except to a close relative. States ban the transplanting of organs from death row prisoners, and occasional moves by some states to ease the ban have failed.
Though few involved in China's transplant trade, from doctors to government ministers, talk openly about it, Beijing has begun to respond to criticisms.
Twice in the past two years, Vice Health Minister Huang Jiefu has publicly acknowledged that China routinely removes organs from executed prisoners for transplants - but only with prior consent.
This month the State Council, China's cabinet, formalized Health Ministry rules issued last year that ban the sale of organs and require donors to supply written permission.
But the regulations do not mention prisoners.
Outside the prison population, voluntary organ donations are rare. China's Confucian heritage holds that the body be kept intact out of respect for parents and ancestors.
Health officials say the country faces a severe organ shortage, estimating that 1.5 million people need transplants in China each year, and that only about 10,000 operations are carried out.
But China's high number of executions - at least 1,770 people in 2005, according to Amnesty International - means organs could be readily available.
Wealthy Chinese and foreigners are willing to pay hundreds of thousands of dollars. Brokers stand ready to arrange transplants in weeks rather than the months or years it often takes in the West. It raises a question: Might China be executing prisoners to stock the organ market?
"There's a very clear demand, and where there's a demand, there's a market," says Henk Bekedam, head of the World Health Organization's China office. "This is a market that needs to be very strongly regulated in order to guide it properly."
Earlier this year, Chinese Foreign Ministry spokeswoman Jiang Yu said that "the use of organs from executed people is done very prudently."
"We have relevant rules and regulations requiring the written consent of the individual donor and the ratification of relevant health departments and courts," Jiang said. "The policy of the Chinese government is very strict."
In the case of Meng's son, city and court officials in Xi'an did not respond to repeated fax and telephone requests for details. The Health Ministry refused to answer a faxed inquiry, referring all questions to its Web site, which only provides general health information and never goes into specific cases.
Meng says her son, Wu Zhenjiang, did not mention donating his organs in his five-page handwritten will, handed to her by court officials after he was executed by gunshot (the most common method in China although lethal injection is gaining ground).
"It's part of his body. It's something he definitely would have written in his will if he wanted to do it," she said.
One family from a village outside the northern port city of Qinhuangdao detailed the horror of seeing their executed son's mutilated corpse.
"His right eye was gone and there was a two-centimeter (0.8-inch) cut on the eye socket. They say it was a gunshot," wrote Ri Chunfen and Ma Yujun in a letter to The Associated Press. "We also found a long cut on his stomach which was sewn up. The court official finally admitted that a liver and two kidneys had been taken away."
The account appears consistent with a report by Human Rights Watch, which quoted an unnamed former Shanghai police official as saying he witnessed the execution of a prisoner whose corneas were needed for a transplant.
"In order to preserve the eyes, the prisoner was shot in the heart," the New York-based rights group quoted the official as saying. "This is what happens. If they need the heart, the prisoner would be shot in the head instead."
Foreigners who have had transplants in China have become part of an uncomfortable debate.
Eric De Leon, a 51-year-old construction superintendent from San Mateo, Calif., received a liver transplant in Shanghai last year. He then found himself criticized by readers of his Web log and by a columnist for Real Clear Politics, a political Web site, for supporting China's organ trade.
De Leon defended his actions, saying that he was unaware of any controversy before his surgery. He said doctors told him the liver was from a 20-year-old heroin dealer killed in a border skirmish.
"I don't think I did anything wrong, to be honest," De Leon said in a telephone interview.
"If a person died just for me, I'd feel bad. But if a guy was a murderer or died in a motorcycle accident or a car accident and a liver came open, so be it." For Meng, the issue also breaks down clearly. "All I want to know is what happened to my son," she says. "I gave birth to him, I raised him. Why didn't they let me see him one last time? Why didn't they let me say just one word to him?" Athletic and with a thick head of dark hair, Wu was a blood donor and a member of the youth league in Kuitun. He came to Xi'an in 2003 to study when he was 24, and worked part-time in an Internet cafe to support himself and send money home. One spring night in 2004, Wu refused entry to a group of men who didn't want to pay for using the computers. The next day, they came back. A fight ensued, spilling onto the street, according to court documents Meng read. Wu, his face bloodied and his fingers broken, pulled a fruit knife - a gift from his mother - and stabbed wildly at his attackers. One man died and another three were injured. Except for a brief court appearance in 2004, Meng never saw or spoke to her son again. Court documents show he was convicted of causing intentional harm and executed Jan. 13, 2005. She began her quest shortly after, and in August that year, she says she got to talking to an elderly man outside a Xi'an government building who told her he was a retired judge and offered to help. He said her son's body had likely been taken to a hospital for his organs. For 600 yuan ($77), he would help get her an audience with a court officer. Meng handed over half the amount - and never saw him again. But the seeds of doubt had been sown. Her suspicions hardened last year while in Beijing where she met a human rights activist. On their January trip to Xi'an, Meng and her 26-year-old daughter, Wu Junjie, rented a cramped, unheated room in a boarding house for $2.50 a day. They can barely afford bus fare and live on noodles and apples from their orchard. Bundled against the winter cold in layers of wool and bounced between city and provincial courts and lawyers' offices, their frustration grows. "They've been kicking responsibility around like a ball. They've been kicking me from one department to another," Meng says. At the Shaanxi Provincial High Court, Meng and Wu are asked to wait in the parking lot. Zhang Wei, a court official Meng has met before, eventually comes out to talk to them. He listens to Meng, who grows agitated and starts shouting and crying as she tries to explain her son's case. They are sent away after 20 minutes with Zhang's office number and a promise that he will "look into it." Three days after they arrive, Meng and her daughter go to one of the city's main crematoriums. There workers tell them that Wu Zhenjiang's body was brought in by a van from Xi'an Jiaotong University's School of Medicine. It was tagged No. 207. At the kidney transplantation center at a hospital affiliated with the school, Meng and Wu meet an unidentified man puffing on a cigarette, who says he had a kidney transplanted there seven years ago from an executed prisoner. "How do I know? It's an unspoken truth here," he says. "If you have money, anything is possible." A hospital official who would give only his family name, Huang, insisted that all organs came from family members. "We never did any organ transplant where organs came from other sources. We never did a transplant where organs came from executed persons," Huang says. "We have never heard of the case of Wu Zhenjiang."