A legal loophole means HIV home testing kits which are banned in the UK can be bought on the internet for just under £30.
Companies which sell the tests, which work by taking a tiny sample of blood from a pin prick, claim they are more than 99% reliable.
But UK doctors say they are not as good as tests carried out in a laboratory, and people who are worried should go to a clinic for a free confidential test.
HIV expert Professor Jonathon Weeber has his doubts about the accuracy of the self test kits.
"You'd have to be pretty familiar with test tubes and things to be able to do this quickly. They're not easy to deal with, and I think would be very difficult to use accurately."
It is illegal to sell the kits in Britain because the government thinks everyone having an HIV test should get counselling to help them deal with the consequences.
A leaflet supplied inside the kit says a positive result must be confirmed by a second test at a laboratory.
Confidential test
Charles Dupont, the owner of one Malta-based website which sells the tests, told BBC's Newsbeat that people in the UK had a right to purchase the kit.
He said: "We are providing a public service and people in Britain should be allowed to buy it."
Colin Dixon, from the Terrance Higgins Trust, says it is much easier to have a free, confidential test at a sexual health clinic.
"If you go to a clinic you have access to counsellors and doctors so you can talk through your future options with professionals, with people who've dealt with this hundreds of times before.
"If you're at home on your own and you find out you're HIV positive then where do you go? Who do you talk to?
"There's no reason to pay $37 for one of these tests when you can get these tests done professionally, accurately in a free clinic."