Health Minister Humberto Costa said on Thursday that tests are meant to identify people who are HIV positive, many of whom do not know or ignore the fact that they have the virus that causes AIDS.
"Some 400,000 people in Brazil don't know about their situation," said Costa. "As well as not treating themselves, they put other people's health at risk."
Brazil is believed to have 600,000 people who have the AIDS virus.
But the World Health Organisation said it considers Brazil's anti-AIDS programme to be a model for other poor nations. Brazil offers some free anti-AIDS drugs and successfully battled rich countries last month to force drug companies to slash prices.
"Some 400,000 people in Brazil don't know about their situation, as well as not treating themselves, they put other people's health at risk."
Humberto Costa, Brazilian Health Minister
Using slogans like "Find out!" and "If you had sex without a condom, take the AIDS test," Brazil will roll out the test campaign this weekend in media advertisements and on posters and stickers plastered across Latin America's largest nation.
The free tests will be done in public hospitals and the campaign has a goal of 3.6 million tests by the end of 2004.
One ad will show people trying to carry pianos through a crowd, symbolizing the doubt on their minds.
"Get that weight off your mind," says the TV ad. Other ads are specifically aimed at prostitutes, pregnant women, married women and parents worried about their children.
While Brazilian men used to be most at risk for AIDS, figures show the disease is now spreading fastest among poor women between 13 and 29 years of age.