The National Zoo says panda mother Mei Xiang is showing a spike in hormone levels, a sign that she might be pregnant again.
But there's no reliable pregnancy test for pandas, and this could be a false alarm.
Mei Xiang was artificially inseminated in March with semen from Tian Tian, the zoo's male giant panda. Test results Thursday indicate Mei Xiang will either give birth or come to the end of a false pregnancy in mid- to late July.
Mei Xiang gave birth to her first cub, Tai Shan, in July 2005, helping to boost zoo attendance and create numerous new panda fans.
Scientists tried to artificially inseminate Mei Xiang last April with semen taken from Gao Gao, a giant panda at the San Diego Zoo. But they later determined she was not pregnant.