Retired slugger Mark McGwire has refused to identify Major League baseball players who use steroids.
McGwire, one of six current and former stars appearing before the House Government Reform Committee, did not say if he used steroids himself.
The retired Jose Canseco said he used them while current stars Sammy Sosa and Rafael Palmeiro said they did not.
The Centre for Disease Control claims 500,000 American teens take steroids to emulate sports heroes.
McGwire, who ranks sixth in Major League history with 583 home runs, said: "Steroids are wrong. Don't take them. It gives you nothing but false hope.
"What I will not do, however, is participate in naming names and implicating my friends and teammates."
Former batter Canseco wrote a best-selling book which claimed steroids were rampant in baseball. In it he wrote that he injected McGwire.
"There's a cloud over the game"
However, Canseco told the hearing he could not fully answer its questions because of concerns his testimony could be used against him.
Earlier, US Senator Jim Bunning, a major league player for 17 years, said: "Baseball needs to know we are watching.
"They owe it to all of us to prove they are fixing this terrible problem. If not, we will have to do it for them."
Committee chairman Tom Davis said: "Kids aren't just talking about their teams' chances in the pennant race, they are talking about which pro players are on the juice."
Committee ranking minority member Henry Waxman said: "We're long past the point where we can count on Major League Baseball to fix its own problems.
"For 30 years, baseball has said, 'Trust us'. The league hasn't honored that trust and it hasn't acted responsibly to protect ball players."
Davis hinted that lawmakers could consider revoking Major League Baseball's anti-trust exemption which, under US law, allows it to be largely self-regulating.
"There's a cloud over the game," he said.
"Maybe we're partly to blame in implicitly and wrongly sending the message that baseball's anti-trust exemption is also a public accountability exemption."
MLB fought attempts to compel players to testify, but they were threatened with contempt charges if they did not appear.
Baseball claims it is doing more than ever to stamp out steroid use, but critics argue its new testing policy and the punishments it can invoke are not tough enough.