A man who ordered a Kindle electronic book reader received a patient's tumour sample instead in a courier delivery mix-up.
James Potten said when he opened the FedEx package the box was marked as "patient tumor - specimen enclosed".
Mr Potten, 37, of Cotham, Bristol, received a parcel from an address in California which was supposed to go to the Royal Free Hospital in London.
"When I opened it I had quite a shock," he said.
The Royal Free Hospital said it was aware that a package "intended for one of its institutions... was delivered to an address in Bristol".
"If [we were] the intended recipient... we will await answers from the delivery company as to how this mistake was made," it said.
FedEx said it "regretted the error" and "will consider future changes to our processes".
Mr Potten said the company contacted him on Thursday to say it had tried to deliver the package, but he was not at home.
He said he called the company and the driver returned to his house.
Mr Potten, an environmental consultant, said: "My name was on the outside, but the contents weren't what I expected.
"I haven't opened the sealed box, which says exempt patient tissue, as it doesn't belong to me. The tracking code on the item had the same first five and last three numbers as my order but it wasn't my Kindle.
"I've been trying to get FedEx to collect it as it is potentially a sample that needs to be tested and sent back with some urgency. I don't know where my Kindle is, but if it is at the Royal Free I'd be happy to do an exchange."
A FedEx spokeswoman said on Sunday the company had retrieved the package and are "delivering it to the correct address today."