The UK's only female giant panda will be ready to mate next week, her keepers predict.
Experts at Edinburgh Zoo have been monitoring Tian Tian for months and have recorded the first increase in her oestrogen levels and a dip in her progesterone.
They now believe she will be able to mate next Tuesday or Wednesday.
Female pandas ovulate once a year, giving a narrow window of 36 hours in which they can get pregnant.
Iain Valentine, director of research and conservation, said: "We've seen behavioural changes in Tian Tian over the last week or so: calling out to Yang Guang, going up to the grate between the two enclosures and spending time in her pond to cool her internal system down.
"And now her hormone levels are changing too.
"Based on the data we have, we believe our female panda will probably be ready to mate early next week, likely on the Tuesday or Wednesday."
The zoo said it is likely that both pandas will be taken off display for some or all of Tuesday and Wednesday. Visitors who have booked a viewing slot will be refunded or be able to rebook for a later date.
Mr Valentine said staff at the zoo are looking forward to next week "with a mixture of excitement and anticipation".
He added: "We have hopes that they will breed but it's totally up to them. On day one both pandas will be put into the same enclosure, with Yang Guang going to Tian Tian.
"Likely only for around 15 minutes, our expert keepers will be on hand to separate the two bears if the sparks fly just a little too much, as at the end of the day, both are powerful and dangerous animals and it's not uncommon for pandas to attack each other after or instead of mating.
"We will introduce them up to three times on the first day. If all goes well, we will continue to encourage natural mating on day two as well. If natural mating doesn't occur on day one, we will consider artificial insemination.
"We are hopeful of a positive outcome. However, we are realistic that this is only the very first year that Tian Tian and Yang Guang have been in Scotland and that we also have 10 more to go!"
Giant pandas Tian Tian (meaning Sweetie in English) and Yang Guang (Sunshine) arrived in Scotland from Ya'an reserve in Chengdu, China on December 4 last year. They went on show to visitors for the first time on December 16.
Earlier this month the zoo said it may stream any birth live on the internet. The panda enclosure has a camera already installed, allowing people to watch the animals every day.
Mr Valentine said: "If Tian Tian does get pregnant, confirmation of this may also not be straightforward. Female pandas often have pseudo-pregnancies where their behaviour and hormones indicate they are pregnant for fairly long periods of time when in fact they're not.
"Also, experts do not know how long panda gestation periods actually are, as female pandas practice delayed implantation. Panda pregnancies can be anything from 85 to 100 days.
"If Tian Tian and Yang Guang mate next week, it might not be until mid-July before positive or negative results can be confirmed.
"We understand that the whole country is in a state of heightened anticipation but whatever the outcome of next week, we as animal conservationists and scientists have learnt a huge amount in such a short time about this captivating species.
"We are just delighted to be playing our part in the essential long-term worldwide panda breeding programme."
Edinburgh Zoo is home for the pandas for the next 10 years.
Tian Tian and Yang Guang are the first giant pandas to live in the UK for 17 years.