Fans hold up a sign which reads 'Got Steroids?' during the game between the New York Mets and the San Fransisco Giants in 2004.
Bonds is charged with four counts of lying to a grand jury when he said that he never knowingly took steroids from his childhood friend and personal trainer Greg Anderson.
On Tuesday, Jason Giambi, his brother Jeremy and former Giant Marvin Benard took the stand and openly admitted they used steroids.
The Associated Press declared it as the biggest mass confession to steroids use in baseball history. All three said they used performance-enhancing drugs purchased from Anderson.
Benard, whose only big league team was the Giants (1995-2003), had a lengthier history with Anderson. After bringing back veterinary steroids he had used while playing winter ball in Mexico between the 1998 and 1999 seasons, he said Anderson told him "there was better, cleaner stuff I could use."
On Wednesday, former New York Yankee Randy Velarde took the stand and testified he also purchased human growth hormone from Anderson. Velarde said it gave him more "endurance and strength'' and said Anderson would help him inject the performance-enhancing drug.
The 48-year-old Velarde said he wanted to work with Anderson specifically because of his connection to Bonds.
Prosecutors hope to use the players' testimony to undercut Bonds' position that Anderson misled him into using steroids by telling the seven-time MVP they were legal supplements.
Anderson is not hearing any of this testimony. He is in jail on contempt of court charges for the duration of the trial for refusing to testify.
The trial was expected to last two to three weeks and is in its second week.