The Edinburgh Zoo pandas Yang Guang and Tian Tian may have "one last time" together after they came "closer than ever before" to mating on Wednesday night.
Hopes of a baby panda being born in the UK this year were fading after the country's only bears failed to mate for a second day despite "natural sparks" flying between them.
The pair met five times on Tuesday, and "several times" again on Wednesday, but an evening rendezvous proved more successful.
An Edinburgh Zoo spokeswoman said that the pandas had met again twice in the evening and the zoo could try to mate the pair "one last time" if the female panda's hormones still showed signs she would be receptive to mating.
She said: "The pandas met again twice this evening and on their first meeting came closer than ever before to mating.
"If Tian Tian's hormones are still partially elevated, we may put Tian Tian and Yang Guang together for one last time early tomorrow morning."
Iain Valentine, director of research & conservation at the zoo, said: "Each time the pair met we saw a huge amount of eagerness and attraction between Tian Tian and Yang Guang.
"There was lots of vocalisation and encouragement from our female and physical contact between the two. He mounted her several times, however full mating did not occur.
"Although both have bred before and have borne cubs with other pandas, they are both still relatively inexperienced. At the end of the day, this is year one of a ten-year conservation project here at Edinburgh Zoo.
"We are hugely encouraged by how much the natural sparks flew between the two animals, as like humans, not all male and female pandas are attracted to each other. Both were keen to mate but their inexperience showed.
"Baby cubs would have been a bonus this year but we have to appreciate that the pandas have only just arrived and have had limited time to settle.
"Overall, we remain very pleased with the outcome of the last few weeks and it has been a fantastic trial run here at Edinburgh Zoo.
"As animal conservationists and scientists, we have learnt a huge amount in such a short time about this captivating species and we look forward to the next ten years."
Giant pandas Tian Tian (meaning Sweetie) 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.