SAN FRANCISCO -- Former Yankee Jason Giambi testified Tuesday that Greg Anderson, the jailed former trainer of Barry Bonds, provided him with performance-enhancing drugs and instructions in their use.

Giambi, the 2000 American League MVP when he was with the Athletics; his younger brother Jeremy; and Marvin Benard, onetime Giants teammate of Bonds, appeared on the witness stand in Bonds' perjury trial.

The prosecution seemed to have an advantage on a day lacking the drama of Monday, when Kimberly Bell, Bonds' former mistress, testified against the home run king.

First, former Giants trainer Stan Conte said he tried to have Anderson and another Bonds trainer, Harvey Shields, banned from the clubhouse. Conte testified he noted Bonds had gained weight and developed acne, which prosecutors contend was the result of steroid use.

Then Jason Giambi told the jury in U.S. District Court that Anderson mailed him injectable testosterone and the infamous cream and clear, undetectable steroids produced by Bay Area Laboratory Cooperative (BALCO).

Jeremy Giambi's testimony virtually duplicated Jason's, confirming Anderson told them what the substances were. "I understood it was a steroid,'' Jeremy said.

Anderson is a key figure in the case, which resulted from Bonds' telling a grand jury in December 2003 that he never knowingly took steroids. Anderson last week was put behind bars a third time for refusing to testify against Bonds.

Bonds, 46, who left baseball after 2007, set the single-season home run record with 73 in 2001, and the career mark, 762. He is charged with four counts of lying and one of obstruction of justice. To convict on perjury, the prosecution must prove the defendant was "knowingly lying.''

Conte, now a trainer with the Dodgers, said Bonds in 2003 acknowledged Anderson was dealing steroids. "Greg was only selling steroids to help his kid,'' is what he said Bonds told him.

Jason Giambi said he used a steroid, Deca Durabolin, before traveling with Bonds and other major-leaguers to Japan in the late fall of 2002. But after Bonds had him contact Anderson, he changed his routine.

Said Jason Giambi: "[Anderson] referred to it as an alternative to steroids that would be undetectable on a test.''

One of Bonds' defense attorneys, Cristina Arguedas, in cross-examination tried to show that Jason Giambi did not know for sure what he received from Anderson.

Giambi did acknowledge he told a grand jury he was never expressly told what the "cream'' and "the clear'' were, other than being alternative forms of steroids.

But prosecutor Jeff Nedrow then asked Giambi about several items he received from Anderson, and Giambi replied, "I understood what it was. A steroid.''