Cristiano Ronaldo and nine other Portuguese international players were subjected to random doping tests at their Obidos training camp on Friday, local press reported.
The tests were carried out by anti-doping officials from European football's ruling body UEFA.
The other players tested were Hugo Almeida, Ricardo Quaresma, Custodio, Nani, Nelson Oliveira, Joao Pereira, Ruben Mical, Miguel Veloso and Hugo Viana. All the players were asked to give blood and urine samples.
It is the second time this week Portugal's players have been tested. Several days ago the Portuguese anti-doping agency carried out tests on Euro 2012 squad players at the request of the Portuguese football federation (FPF).
UEFA in recent days has carried out tests on a number of teams participating in Euro 2012, to be held in Poland and Ukraine from June 8 to July 1.