Now, a published report alleges that Bonds, indeed, failed one in 2006, testing positive for amphetamines in the drugs' first year on Major League Baseball's banned substances list.
Giants teammate Mark Sweeney.
Bonds said in a statement last night that he did not get amphetamines from Sweeney, but did not deny yesterday's report that he tested positive for the drugs last season.
"He is both my teammate and my friend," Bonds said. "He did not give me anything whatsoever and has nothing to do with this matter, contrary to recent reports.
"I want to express my deepest apologies, especially to Mark and his family, as well as my other teammates, the San Francisco Giants organization and the fans," he said.
"Obviously, we're pleased that Barry has straightened this out," said Sweeney's agent, Barry Axelrod.
Representatives of MLB and the Major League Baseball Players Association declined to address the report.
"We don't comment on any issues related to the testing program unless they have been announced publicly," said players union spokesman Greg Bouris.
Bonds is the first player to be linked to amphetamines - often referred to as "greenies" and long considered the drug of choice for athletes looking for a quick energy boost - since baseball and its players association prohibited them before last season.
As part of baseball's policy, urine testing for all banned drugs occurs once during spring training and at least one other time each season. There are also randomly selected tests, so some players submit samples three or more times per year.
Unlike steroids, however, testing positive for amphetamines does not result in an immediate suspension or public announcement. First-time offenders receive treatment and counseling and must be tested six additional times within a calendar year, but their names remain confidential throughout that process.
It's not until a second amphetamine offense that a 25-game suspension is issued and publicly announced. According to the policy, a player would be suspended 80 games for a third failure and would receive an indefinite suspension, which could include a permanent ban, for a fourth.
In contrast, a first failed test for steroids includes a publicly announced 50-game suspension, 100 games for a second failure and a lifetime ban for a third.
The difference in severity has as much to do with the unknown as the public perception that steroids are more destructive to the game than amphetamines, according to one industry source familiar with the subject.
Believing that greenies were a problem, baseball officials and the union agreed to the ban, the source said. But because it was impossible to determine how many failed tests would occur in the first year - whether it would be a handful or an embarrassingly large number - the sides agreed it would be best to keep the information confidential.
Neither the union nor the players association would reveal how many players tested positive for amphetamines in 2006.
Three players on the 40-man rosters of big league clubs - New York Mets pitchers Yusaku Iriki and Guillermo Mota and the Arizona Diamondbacks' Jason Grimsley - received 50-game suspensions for steroid use or involvement last year.
A dozen players, including the Orioles' Rafael Palmeiro, tested positive for steroids in 2005 and received 10-day suspensions. Stiffer penalties, as well as a more detailed banned list, were adopted after the 2005 season.
Bonds, 42, has been the subject of a federal steroids probe since 2003, when agents raided the home of his personal trainer as well as the Bay Area Laboratory Co-Operative in suburban San Francisco.
The controversial outfielder agreed in principle to a one-year, $16 million contract with the Giants in December, though it won't be finalized until specific contractual language is agreed upon. Bonds is 21 home runs away from tying Hank Aaron (755) for most all-time.
The Associated Press contributed to this article.