Major League Baseball players and owners have agreed on a tougher anti-doping programme for the sport.
The new regime includes penalties for first-time offenders, expanding the number of banned substances and random, year-round checks.
The move is a response to a series of allegations that hit baseball in 2004.
Baseball stars Barry Bonds and Jason Giambi are both caught up in the Balco steroid scandal that has rocked the American sports world.
"We have agreed on a new, much-tougher drug-testing programme that is designed to rid the game of performance-enhancing drugs," MLB commissioner Bud Selig said.
"I have been saying for some time that my goal for this industry is zero tolerance regarding steroids.
"This agreement is an important step towards achieving that goal. We are acting to help restore the confidence of our fans in our great game."
A first positive test for a steroid would result in a suspension of up to 10 days, a second positive test a 30-day ban, a third positive a 60-day penalty, and a fourth positive test a one-year ban.
Under the previous regime agreed in 2002, a first positive test resulted only in treatment, and a second positive test was subject to a 15-day suspension. Only with a fifth positive test was a player subject to a one-year ban.
In addition to one mandatory test for every player each season, players will randomly be selected for additional tests, with no maximum. Players will also be randomly selected for testing during the off-season.
Human growth hormone, the substance at the heart of the Balco scandal, was added to the list of banned substances, which includes steroids and diuretics.
The new sanctions fall short of World Anti-Doping Agency guidelines where offenders are banned for two years on a first positive test then banned for life after a second, though both MLB and the players' union defended the new policy.
"Our goal was to come up with something that we believe will take care of the issue and solve it," said players' union head Don Fehr.
"The object is to stop it, not to penalise for the sake of penalising.
"With the enhanced testing and enhanced disciplinary levels, I will be very surprised if this doesn't take care of the problem."