SAN FRANCISCO – A federal judge in the perjury case against Barry Bonds on Tuesday decided to allow an audio recording in which, prosecutors say, the baseball star's personal trainer discussed his steroids use.

Bonds' lawyers had asked the judge to exclude the recording from his upcoming trial on charges that he lied to a grand jury when he said he never knowingly took performance-enhancing drugs. They argued that since the personal trainer, Greg Anderson, is refusing to testify, there's no way to authenticate the topic of discussion.

But prosecutors plan on calling to the witness stand Stevie Hoskins, Bonds' childhood friend and former business partner. Hoskins says he secretly recorded the conversation in March 2003 to convince Bonds' father that his son was taking steroids.

The trial is scheduled to start March 21.

The judge also refused to throw out one of the five charges alleging Bonds lied to a grand jury in December 2003 when he testified he never knowingly took steroids.

His lawyers complained that the charge was too vague. The charge alleges Bonds' testimony obstructed the grand jury's investigation into sports doping.

The judge ruled the charge was specific enough for Bonds to mount a defense during his month-long trial.