Burglars stole medical equipment worth more than £160,000 from the John Radcliffe Hospital in Oxford.
Four endoscopes - tiny cameras used for medical examinations - and other equipment were taken from a ward between 11pm last Thursday and 7am the following morning.
Detectives said the cameras, worth about £28,000 each, could end up being shipped overseas.
Dc Tony Maddison, of Oxford police's burglary team, said there were no signs of a forced entry but there was "nothing to suggest" anyone working at the hospital was involved.
"Things like this have happened at other hospitals in other areas," he added.
A hospital spokesman said: "These are valuable pieces of equipment, and we would appeal to anyone with any information to help the police with their inquiries.
"We would like to reassure patients that services continue as normal. However, this incident does put additional pressure on our staff, and we would very much like to see the equipment returned."
Anyone with information should call Oxford police on 08458 505505, or the free anonymous Crimestoppers line on 0800 555111.
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