Opening statements began Wednesday in Washington, D.C. in the trial of baseball star Roger Clemens.
He is accused of lying to Congress about his use of steroids.
Assistant U.S. attorney Steven Dunham said that about 45 witnesses, including several of Clemens' former teammates, will help make the case against him.
"We will prove that Mr. Clemens. used anabolic steroids and human growth hormone," Dunham said.
When Clemens denied the use in 2008, Dunham said, "It was false and he knew it was false."
Clemens was indicted last August on charges of obstruction of Congress, perjury and giving false statements.
He denied using performance enhancing drugs, specifically steroids and human growth hormones.
Clemens maintains that he didn't use any kind of drug during a 24-season career in which he set several pitching records.
The jury made up of 10 women and two men were told to avoid news and sports programs. They can read newspapers that have been screened at the courthouse to remove any reference to the case.