Health authorities in Washington DC are launching a pioneering scheme to promote HIV testing.
Aids activists say authorities may not be able to cope with the results
The authorities hope the scheme will lead to tests becoming routine across all health services in the District of Columbia from schools to hospitals.
It will target everyone aged between 14 and 84 and is thought to be the US's most aggressive such testing campaign.
The district has the US's highest Aids rate and new figures show 4% of residents have HIV, officials said.
"This is public issue number one," said health director Gregg Pane as the latest infection figures were released on the on the eve of the campaign, the Washington Post reported.
The authorities are distributing 80,000 rapid testing kits which just use a mouth swab, not a blood test, and give results in 20 minutes.
These are being handed out to a range of medical centres, including schools, community health clinics and hospital.
Testing still needs the individual's consent - but it is thought to be the biggest testing drive the US has yet seen.
AIDS IN THE US
1m Americans have HIV
40,000 infected each year.
About a quarter of those infected are unaware
A total of 16,165 Aids cases were recorded in Washington DC between 1981 and 2004.
Officials are now estimating as many as 25,000 may have HIV in the district.
"That's a huge number," said Marsha Martin, senior deputy director of the DC Administration for HIV Policy and Programs, the Post reported.
It is thought that roughly a quarter of those in the US with HIV do not yet know they are infected.
Early detection also makes a big difference to how effective treatment can be.
But the BBC's Jill McGivering says some of those working with people with HIV or Aids are sounding a note of caution about the campaign.
They are anxious that counselling and support services will not cope if there is a sudden flood of people with positive tests, she says.
But the authorities insist they are prepared. The 20-minute wait for results is used for initial counselling, they told the BBC, and talk about risk and sexual behaviour.
Anyone who tests positive is then referred for specialist medical care and will have further counselling as part of that, they say.
The Centers for Disease Control and Prevention in Atlanta estimates that more than one million Americans have HIV and about 40,000 people are infected each year.