Several thousand bees that were part of a multi-million pound research project in Dundee have been stolen.
The British black bees, worth between £3,000 and £3,500, were taken from the grounds of the city's Ninewells Hospital on Sunday morning.
They were contained in four hives and were being used in a £2m neuroscience study at Dundee University.
The lead researcher on the project, Dr Chris Connolly, said the thieves must have known how to handle bees.
"It is very disheartening that this has happened and, whilst we are still taking stock of the full implications if the bees are not returned, this theft will undoubtedly hamper our research," Dr Connolly said.
"The bees were there when I arrived at work on Sunday morning but were absent when I went to work on them 20 minutes later.
"Two middle-aged men in a white van were seen pulling up beside the hives at this time and clearly whoever did this knows what they were doing and how to handle bees."
Dr Connolly said the bees were unique and should be easy to identify.
It is not known whether they were stolen for their breeding potential or for another reason.
The study was investigating the potential effect of pesticides on bee learning and health.
The scientist added: "This is very important research given the decline in honeybee numbers so I would urge anyone with information to get in touch with the police."
The cedar wood hives, made by Thorne, were taken from the grassy area to the south of the East Block at Ninewells Hospital.
Tayside Police said they were keen to trace a white box van and two men that were seen in the area some time before 1000 BST on Sunday.
One of the men was wearing a bonnet.