Hsing-Hsing, the surviving male of a pair of giant pandas who had enchanted visitors to the National Zoo since 1972, was euthanized yesterday after keepers decided that his worsening kidney disease was making him suffer too much.

He and his mate, Ling-Ling, had been the zoo's best-known and best-loved animals since they arrived in Washington under armed guard as a gift from the Chinese government after President Richard M. Nixon's historic visit to China. People lined up to watch them frolic, listened avidly for news of their mating attempts, rejoiced when cubs were born, sent sympathy cards after each of their five offspring died, and mourned when Ling-Ling died of heart failure in 1992.

Hsing-Hsing was 28 years old, the equivalent of more than 80 in humans. By the time he died, zoo officials said, he barely recognized his keepers and had trouble moving or summoning energy to eat his favorite foods.

Zoo officials said Hsing-Hsing, whose terminal kidney disease was diagnosed in May, began declining markedly during the past week. Zoo administrators, veterinarians and keepers agreed Saturday to euthanize him but wanted to first offer him a last meal of the treats he liked best. The zoo's chief veterinarian, Lucy Spelman, gave the fatal injection yesterday about 7 a.m. in the Panda House.

"It became clear to us that we could not maintain his quality of life," Lisa M. Stevens, the associate curator of primates and pandas, who had cared for the animals for 13 years, said at a news conference. "Everything became an effort for him."

Giant pandas are extremely rare, and their cute black-and-white images have become international symbols for conservation. Hsing-Hsing's death leaves five giant pandas in U.S. zoos--a young pair on loan in Atlanta, and an adult pair, with a 3-month-old cub, on loan in San Diego.

There are about 120 more giant pandas in other zoos around the world and only an estimated 1,000 in the wild. The pandas, found in the bamboo-forest mountains of China, are endangered because of declining habitat and poaching.

The Panda House will be kept open for educational purposes, officials said. The National Zoo has asked China for a long-term loan of a breeding pair of pandas, but negotiations have stalled over money: The zoo has offered $2.5 million over 10 years, and China has said it wants at least $8 million.

The Friends of the National Zoo has begun a Giant Panda Conservation Fund with the goal of raising $250,000 a year for the next decade to help bring pandas back to the nation's capital.

Zoo veterinarians and pathologists spent most of yesterday performing a necropsy on the elderly panda. His skin and skeleton, like those of his mate, will be donated to the Museum of Natural History. His organs and tissue will be kept for further study.

At the Panda House, someone placed a single iris at the panda statue along the walkway leading to the exhibit. Handwritten signs at each of the two doors told visitors that Hsing-Hsing had died. A memorial photo of him was set up on an easel inside his enclosure, and the zoo's Web site, www.si.edu/natzoo, included "Hsing's final update" and other information about him.

Yesterday morning, fresh bamboo was carried out of the Panda House--to give to the camels.

Keepers, including Stevens, were visibly upset. Some visitors dabbed tears from their eyes as they learned the animal had died.

Sarah Gibson used to visit the Panda House often when she lived in the Washington area. Yesterday, making her first visit to the National Zoo in five years, she brought her 23-month-old daughter in hopes of showing her the fuzzy bear.

"There was something very--I don't know--touching about the panda story," said Gibson, 34, who now lives in Bloomfield, Conn. "I spent a lot of time walking through the exhibit and reading all the information. He was always just a favorite. He seemed like such a sweetheart."

Donna Neish, of Pittsburgh, gasped when she saw the sign announcing the panda's death. She and her husband, Larry, were in town for the holiday weekend and visited the zoo for the first time. Their children, 7 and 4, had raced up the walkway to the Panda House.

She could not bring herself to tell her children. "Ah," she said, recovering from her shock. "How sad. The panda ran away."

Hsing-Hsing, whose name means "shining star," had been in failing health for several years. In 1997, both of his testicles were removed after one was discovered to be cancerous. He developed arthritis, which was controlled by medication hidden in his favorite treat--blueberry muffins from Starbucks. His eyesight was going. He had mysterious nosebleeds.

When the terminal kidney disease was found, keepers kept their charge comfortable by flushing his organs occasionally and giving him other medication. But over the past week, they said, he seemed increasingly lethargic.

He did not want to go outside. He ate less and less and afterward would lie down exhausted. Sometimes, he could not even get up when he urinated or defecated. His weight, taken just last week, was 249 pounds--down from his prime of 290.

Despite an iron shot on Tuesday, his gums were pale from anemia related to his kidney problems. Blood samples--collected from his nosebleeds--showed he was so ill and anemic that flushing his kidneys wouldn't help him feel better.

With zoo director Michael Robinson in London, keepers and veterinarians alerted deputy director McKinley Hudson. He said he looked in on Hsing-Hsing on Friday and saw the animal take only a few steps before having to lie down.

On Saturday, after consulting with the panda's three day-to-day keepers, Spelman and Stevens called Hudson at home. They told him they had all agreed the animal should be euthanized. Hudson agreed.

"It's kind of an end of an era," he said he told them. "It's unfortunate, but it's the best thing to do."

They decided to wait until yesterday morning, in part to give their furry charge one last good night. He usually had the most energy during the afternoons and evenings. They made up a last meal of his favorite foods: baked yams, bamboo, rice gruel and "the biggest blueberry muffin we could find," Stevens said.

She hoped for a miracle when she arrived at the Panda House yesterday shortly after 6 a.m., but Hsing-Hsing's condition hadn't improved. Spelman first anaesthesized the animal, poking him with a long syringe--a detail Stevens winced to recall. Ten minutes later, Spelman gave him a second shot of anaesthesia.

Spelman and an assistant took blood samples from the panda that they hope will help researchers who study his death. Then she inserted an intravenous line into the animal that carried a drug that stopped his breathing and circulation.

There were about 10 to 15 people on hand when it happened, Stevens said, though only the veterinarian and her associates, three keepers and Stevens were actually present in the back of the enclosure when the panda was put down. There was then what Stevens described as "an opportunity to say good-bye" for panda staff members who wanted it.

Zoo officials called the Chinese Embassy in Washington, as well as the China desk at the State Department. They alerted the media. At 8 a.m., they opened the grounds as usual.

The melancholy at the close of Hsing-Hsing's life was in sharp contrast to the excitement surrounding his and Ling-Ling's arrival in April 1972. About 20,000 people came out for the panda pair's first day of public viewing. Initial reports said Hsing-Hsing sometimes had a bad temper, but he proved to be the sweeter of the two.

Attention soon turned to the quest for an heir to bolster the declining panda population--but it was not to be. Female pandas are fertile for at most three days a year. At first, Hsing-Hsing did not seem to know how to mate with Ling-Ling, and she swatted him away. Finally, in 1983, they mated for the first time. A male cub was born--the first in the United States--but died of pneumonia.

From then on, there was an annual waiting game for a cub, eagerly followed throughout Washington. Eventually, Ling-Ling gave birth to four more cubs by Hsing-Hsing. But the newborns were in fragile health, and all died within a few days. Hsing-Hsing's semen was sent once to the Tokyo zoo and three times to the Mexico City zoo in hopes of producing cubs there through artificial insemination. No cubs resulted, however.

Yet even the zoo's failures produced valuable baseline information about giant panda biology and behavior that has helped other institutions care for captive pandas. The zoo's panda experience resulted in more than two dozen research papers on subjects from hormone levels to artificial insemination. And Hsing's death is expected to produce still more scientific information on the physiology of aging.

"We feel immense sadness," Stevens said, "and at the same time immense emptiness--as empty as the Panda House is now."

Staff writer Karlyn Barker contributed to this report.

Panda Era Comes to an End

Key events in the lives of the National Zoo's giant pandas:

April 16, 1972: Hsing-Hsing and Ling-Ling arrive at the National Zoo, a gift from the people of China.

Spring 1976: First unsuccessful breeding attempt.

Spring 1981: Chia-Chia, male giant panda from London, brought in to mate with Ling-Ling, but they fight and he mauls her instead.

March 1983: Ling-Ling and Hsing-Hsing mate for the first time. She also is artificially inseminated by Chia-Chia.

July 21, 1983: Ling-Ling gives birth to a male cub that dies of pneumonia. DNA tests reveal the father was Hsing-Hsing.

December 1983: Ling-Ling nearly dies of a kidney infection.

Aug. 4, 1984: Ling-Ling gives birth to a stillborn male cub.

June 23, 1987: Ling-Ling gives birth to twins. One dies immediately and the other lives for only four days, the longest of any cub at the zoo.

Sept. 1, 1989: Ling-Ling gives birth to a male cub that soon dies.

Dec. 30, 1992: Ling-Ling dies of age-related heart failure.

April 2, 1997: Hsing-Hsing is discovered to have testicular cancer; surgery to remove testicles is successful.

May 15, 1999: Hsing-Hsing is discovered to have kidney disease.

Yesterday: Hsing-Hsing euthanized.

Source: National Zoo