Barry Bonds, Major League Baseball's all-time home run leader, pleaded not guilty on Friday to charges stemming from testimony he gave to a federal grand jury in San Francisco four years ago.

The case has long led to much debate as to the validity of the charges against Bonds, and if his case goes to trial, it will draw more attention than any legal case in the history of baseball.

Here are answers to some questions about Bonds, the charges against him and what may lie ahead.

What are the charges against Bonds?

Four counts of perjury and one count of obstruction of justice for allegedly lying about his use of performance-enhancing drugs in testimony given to a grand jury four years ago.

What penalties are associated with those charges?

Legal analysts generally agree that Bonds, who would be a first-time offender, is facing a maximum of 30 months in prison if convicted of all counts.

Why has Bonds been charged when other athletes have used steroids?

Bonds hasn't been charged with using performance-enhancing drugs; he's been charged with lying to a federal grand jury about taking those drugs. The grand jury was investigating BALCO, not Bonds, and Bonds was given immunity from prosecution when he testified to the BALCO grand jury four years ago -- on the condition that he tell the truth. The Yankees' Jason Giambi, for example, admitted using steroids when he testified to the same grand jury. Bonds, however, testified that he never knowingly took steroids and that he didn't know that "the cream" and "the clear" were steroids that mask the use of other steroids.

Prosecutors suspected that Bonds was lying and began an investigation. Three grand juries were involved in that investigation during the past four years.

Drug Policy in Baseball

The testimony of Bonds and Giambi, which by federal law was supposed to remain sealed, was leaked to the San Francisco Chronicle. The lawyer who was found guilty of the leak was sentenced to 30 months in prison.

Bonds isn't the only one who has been charged with perjury as a result of the BALCO case. Track star Marion Jones pleaded guilty to charges two months ago and former cyclist Tammy Thomas has also been charged with perjury and is awaiting trial.

How can the government prove Bonds committed perjury?

Prosecutors are expected to provide evidence in the form of positive steroid tests and other documents, as well as present witnesses who would be expected to support the notion that Bonds indeed knowingly took steroids -- remember that the charges are not that he used steroids but that he lied about it to the grand jury.

Witnesses are expected to include Kimberly Bell, Bonds' former mistress; Arthur Ting, Bonds' personal physician; Steve Hoskins, a one-time friend of Bonds who says he has direct knowledge of Bonds' alleged steroid use; former BALCO vice president James Valente and a number of athletes who have been associated with BALCO.

Prosecutors claim to have a blood test from November 2000 that shows a "Barry B" testing positive for two types of steroids.

Will the case go to trial?

It's expected to. That could change, though, if Bonds and his lawyers see a body of evidence large enough to prompt them to seek a plea agreement. That would likely result in a lesser penalty for Bonds than if the case goes to trial and he is found guilty.

What will be Bonds' defense?

Bonds' lawyers would be expected to challenge the validity of any positive steroid tests and also to attack the credibility of witnesses on the grounds that they have personal motives for testifying against Bonds. They may also attack the process, claiming that the government conducted a witch hunt against Bonds for a variety of reasons, including his public stature stemming from being baseball's all-time home run king.