Britain's only female giant panda is showing signs of pregnancy, Edinburgh Zoo said on Friday.
Tian Tian's protein and hormone levels have changed after she was artificially inseminated in April, keepers said.
Changes in her conduct including lack of appetite, moodiness and "nesting" behaviour have also been spotted.
If Tian Tian does give birth, her cub would be the first ever born in Britain.
She could give birth as early as next month but the zoo is remaining cautious as it has not yet been possible to carry out an ultrasound which would confirm the pregancy as it is too risky to sedate her.
Iain Valentine, director of the zoo's panda project, told BBC Radio Scotland: "The indications are good. What has happened is she has had the secondary rise in progesterone.
"That can mean one of two things—she is either pregnant or she has now entered the period of her pseudo-pregnancy.
"There are more tests to be done, so at this time things are looking good but it can change."
Tian Tian and the zoo's male, Yang Guang—the UK's only pair of giant pandas—arrived in Scotland two years ago after being rented from China.
The animals turned out to be huge crowd-pullers with visits from around 500,000 people in their first year.
It was hoped that the pair would mate naturally but that did not happen after Tian Tian, whose name means "Sweetie", showed signs that she was not "conducive to mating".
If a cub is born at the zoo, it is expected to stay in Scotland for two years before returning to China.
Explore further: Birds 'weigh' peanuts and choose heavier ones