The female giant panda at Edinburgh Zoo may be pregnant, according to keepers.
Tian Tian is showing signs that she may be expecting a cub, the director of the zoo's panda project said.
Iain Valentine told the BBC things are "looking good" after the panda's artificial insemination in April.
Positive signs include changes to Tian Tian's protein levels and an increase in her progesterone hormone levels, the zoo said.
Keepers have also spotted changes in her behaviour, including lack of appetite, moodiness and "nesting" behaviour.
But the zoo is being cautious as it has not been able to carry out an ultrasound and will not know for certain until shortly before the panda gives birth.
If she is pregnant, that could happen as early as next month.
Tian Tian and the zoo's male, Yang Guang, are the UK's only pair of giant pandas.
Keepers had hoped that the pair would mate naturally but that was not attempted as scientists decided that Tian Tian showed signs that were not ''conducive to mating''.
The pandas arrived from China in December 2011 and have been a popular attraction with visits from around 500,000 people in their first year, including actress Nicole Kidman and the Princess Royal.
Mr Valentine said the signs were "hugely exciting", as a baby panda has never been born in the UK.
He told BBC Good Morning 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."
The zoo has been working with a team of international experts to determine whether Tian Tian is expecting a cub.
Mr Valentine said: "The Chinese are central to this. The more work that's done in the West on pandas is all then fed back into China and then it means that the bigger numbers of pandas that they are looking at will then benefit from that."
But Chris West, chief executive of Edinburgh Zoo, told the programme the team was realistic about the prospect of failure.
"It happens all the time," he said. "We have a lot of endangered species, we have the husbandry and veterinary support and we aim to breed them as a genetic reservoir in case they go extinct in the wild.
"We are used to that sense of maybe pregnant, maybe not, we'll see. If she isn't, we will go round again."