Venezuela took part in its first summit meeting of the Mercosur trade bloc as a full member on Friday, but without President Hugo Chavez present.
Sitting in for Chavez at the one-day gathering of South American leaders in the Brazilian capital was Venezuelan oil minister Rafael Ramirez.
Venezuela became was welcomed into Mercosur in July.
Chavez's absence at the meeting raised new questions about his health.
The president returned to Venezuela on Friday after 10 days of medical treatment in Cuba, where he underwent hyperbaric oxygen treatment. Chavez has spent much of the past 18 months under treatment for cancer and has said he's free of the disease.
Present at the meeting were the presidents of the other countries that comprise Mercosur: Dilma Rousseff of Brazil, Argentina's Cristina Fernandez and Jose Mujica of Uruguay.
Paraguay, the other Mercosur member, was not represented because it was suspended in June after the hasty impeachment of then-President Fernando Lugo.
"With Venezuela's entry, Mercosur now extends to the Caribbean and Amazon," Rousseff said in a speech. "As a bloc we are now the world's fifth largest economy, with an enormous energy-generating potential, a huge food producing potential and a substantial industrial park."
During the gathering, Venezuela agreed to adopt the trade bloc's tariffs on 28 percent of goods covered by its trade regime. All products will be covered by 2016.
Also present at the summit was Bolivian President Evo Morales, who agreed to begin talks aimed at having his country become a full member of Mercosur.
"Bolivia's entry will make Mercosur much stronger," Rousseff said.