The home secretary and a host of cross-party MPs have been tested for HIV - to encourage others to do the same.
Amber Rudd took the blood test with Green Party co-leader Caroline Lucas, Public Health Minister Steve Brine and Labour's Liz Kendall to promote National HIV Testing Week.
The Terrence Higgins Trust said early diagnosis could help people with HIV live long, happy and healthy lives.
But figures suggest about 10,700 people do not know they have HIV.
Ms Rudd and a number of MPs had been tested in their parliamentary offices, while others had attended the Terrence Higgins Trust HQ in King's Cross, London, or visited local services in their constituencies.
Afterwards, the home secretary tweeted: "Despite the look on my face, the pain wasn't that bad! Just took an HIV test with Terrence Higgins Trust to raise awareness for HIV Testing Week."
Liam Beattie, the charity's campaigns and parliamentary officer, said: "While we've seen some major steps in HIV in recent years, the number of late diagnoses and undiagnosed people living with HIV is still a cause for concern.
"It's vital that we enable people to feel empowered to test and know their status and dispel the myths that surround testing for and living with HIV, which no doubt support from a number of prominent MPs will hugely help."
National HIV Testing Week, which ends on 24 November, was kicked off by Prince Harry, who attended the opening of a pop-up shop in Hackney, which has been issuing self-test kits for people to use at home.
According to new Public Health England figures, roughly 10,700 people are living with undiagnosed HIV in England.
Terrence Higgins Trust spokesman Matt Horwood said the campaign encourages "everyone to get tested, regardless of sexual orientation or background".
"It's important for all people to have good sexual health and for all people to be tested and screened so they know their status," he said.
"While there might be some people who are completely celibate and think none of this applies to them, they are likely to be a very small percentage and we would still encourage them to take this free test for peace of mind."
HIV can be transmitted through bodily fluids, such as blood, semen and breast milk.
Symptoms for HIV infection include aching limbs, headaches and mouth ulcers, but the Terrence Higgins Trust says treatment is important not only to reduce these symptoms but to help those who test positive live the healthiest life possible and prevent transmission.
MPs who are also taking HIV tests, include: Labour's Sarah Champion, Peter Kyle, Lilian Greenwood, Gareth Snell, Ian Austin, Thangham Debbonaire, Tracy Brabin, Thelma Walker, Ruth Cadbury and Alex Norris, along with Stephen Hammond, Tom Pursglove and Stuart Andrew from the Conservatives.
Mr Kyle, MP for Hove, said: "HIV is a long-term manageable condition and the earlier the diagnosis, the better it is for the patient, so it's important to get tested no matter who you are.
"The fear and stigma surrounding HIV is still a barrier to testing, so I hope I've shown today that having a test is fuss-free and easy and that I can help make the stigma and fear around HIV a thing of the past."