All residents and staff in care homes where someone has coronavirus will be tested, the Welsh Government has said.
Until now only those with symptoms, or who were being moved into a care home, were being tested for Covid-19.
The Welsh Government said the "latest evidence" prompted the change in policy.
But the Welsh Conservatives, who called the decision a "u-turn", said it should be expanded to all care home residents and workers, in line with England.
Under the new policy, those living or working in a care home where someone has tested positive for coranavirus will now be tested, with repeat tests to be done a week later.
Neighbouring care homes may also be tested under a system which will use mobile testing units and home testing kits.
The criteria remains narrower than that in England where all care home staff and residents can be tested.
Earlier this week the Welsh Government was criticised by care workers and opposition parties for not expanding testing to all care home residents and staff.
First Minister Mark Darkeford said clinical evidence showed there was "no value" in testing everyone, and he feared testing asymptomatic people would "divert capacity".
But Older People's Commissioner Helena Herklots criticised the testing criteria saying rules should be changed in line with England as a "matter of urgency".
In Wales, the daily testing rate remains around 1,000 despite there being capacity to carry out about 2,000 tests.
The Welsh Government had been criticised for dropping its target of reaching 5,000 tests a day by mid-April.
In England anyone with symptoms who is over 65, or has to leave the house to work, and others in their households, are eligible for a test.
Tests in Wales have only been available for key workers and anyone in hospital experiencing symptoms.
Health Minister Vaughan Gething, who had previously said testing everyone in care homes was not the best use of resources, said the evidence was under constant review.
"At the moment, the evidence does not support the blanket testing of everyone who does not have symptoms," he said.
"But, in a care home setting, where there are some people who have symptoms of coronavirus and others who do not, testing everyone, including those who do not, does have a purpose - we will be doing this to help manage outbreaks."
Welsh Conservative social care spokeswoman Janet Finch Saunders said the decision amounted to a "u-turn" which would be welcomed by residents and staff and their families.
"Testing can help to reduce the spread of this deadly and horrid virus that is having a devastating impact on the most vulnerable in society," she said.
"We urge the Welsh Government to continue their u-turn and expand testing to all care home residents and staff."
Plaid Cymru leader Adam Price said the new policy was "questionable", and asked: "Why not test staff and residents in every home?".
He called on the Welsh Government to publish its evidence, "so that it can be scrutinised to see how and why it differs from international evidence and best practice that promotes universal testing of all care home staff and residents".