The National Zoo's female giant panda did not want to play outdoors with her mate and spent much of her days sleeping in her den. She collected bamboo, broke it into pieces and made a nest. She cradled an apple in her arms, then a pear.

The bear certainly acted as though she were pregnant, but National Zoo officials announced yesterday that Mei Xiang is not.

Mei Xiang and the zoo's male panda, Tian Tian, did not mate successfully this year, and, as a fallback plan, Mei Xiang was inseminated vaginally May 2. Zoo scientists said they did not expect the procedure to work, and hormone tests this week proved that it had not.

Instead, Mei Xiang had a "pseudo pregnancy," in which she ovulated but failed to conceive, resulting in elevated hormone levels that resemble those during pregnancy. This is common in giant pandas and makes it difficult to tell whether the animal is truly pregnant.

Pandas give birth about three to six months after mating. With Mei Xiang's hormone levels still high, zoo officials added an extra evening shift of volunteers this month to watch for pregnancy-related behavior changes. The panda also received weekly ultrasound examinations, which she had been trained to accept, and the tests showed no evidence of pregnancy.

Mei Xiang's level of one hormone, urinary progesterone, began declining Sept. 5, signaling either that a birth or end of false pregnancy was near. By Monday, the hormone was down to its usual non-pregnancy level, known as the baseline, and zoo officials waited two days to make sure no cub emerged.

"I feel down, but I feel hopeful for next year," said assistant curator Lisa Stevens. "I am looking forward to next year, and it can't come quickly enough."

Things were clearly back to normal yesterday at the Panda House when zoo officials opened the door from the indoor den to let Mei Xiang outdoors again to join Tian Tian.

"She was trying to pull the door open before we opened it," Stevens said. "Once they were together, it was like they had never been apart."

The two giant pandas arrived on a 10-year loan from China in December 2000. Any cubs would be the property of China. The National Zoo had a previous pair of giant pandas, which arrived in 1972, but they never had a panda cub that lived for more than a few days.

Pandas are unreliable breeders; among other things, the female is in heat for only two or three days a year. The National Zoo's pandas mated briefly last year, but no pregnancy resulted. Mei Xiang is 6 and Tian Tian is 7, and they are at the beginning of their mating years.

As their mating window closed in May, zoo scientists vaginally inseminated Mei Xiang with Tian Tian's sperm. The procedure used much less sperm than in natural mating and is less effective than artificial insemination, which deposits sperm into the uterus and would have required anesthesia.

Mei Xiang had a "pseudo pregnancy" -- she ovulated but failed to conceive.