FACTBOX: Rules about steroid use in U.S. sport

(Reuters) - Some of the biggest stars in baseball were named on Thursday in the Mitchell Report -- a far-reaching investigation on the use of performance enhancing drugs in one of the most popular U.S. sports. The report also called for year-round, unannounced steroid testing for baseball.

Following are the current rules regarding steroids in various U.S. sports:

MAJOR LEAGUE BASEBALL

* Prohibits the use of performance-enhancing drugs like anabolic steroids. Amphetamine use is also prohibited.

* Testing in the Major Leagues began during spring training in 2003 but penalties were light. A first positive test would result in treatment and a second would lead to a 15-day suspension. Only on the fifth positive test would a player be banned from playing for one year.

* In December 2005 the baseball players' association approved a proposal by team owners to tighten up the steroid policy. Under new rules, a positive test result causes a 50-game ban without pay. A player would be suspended for 100 games for a second positive test and banned for life for the third positive result, though players can seek reinstatement after a two-year suspension. Rules regarding use of amphetamines were also tightened.

NATIONAL FOOTBALL LEAGUE

* Prohibits the use of anabolic steroids, certain stimulants and human or animal growth hormones in addition to agents known to mask the presence of the drugs in urine.

* All players are tested for prohibited substances at least once during the regular season. Each week during the regular season, 10 players on every team are randomly selected to be tested. In addition, random testing is conducted while preseason games are played. Players under contract may also be tested up to six times during the off-season months.

* A first positive test will result in suspension for at least four games. The second positive test would result in suspension for at least eight games. A third positive results in a one-year playing ban. Suspensions are all without pay.

NATIONAL BASKETBALL ASSOCIATION

* Steroids, diuretics, performance-enhancing drugs and masking agents are all prohibited substances.

* All players are subject to four random tests each season.

* A player can come forward voluntarily if he is using a prohibited substance to get treatment without penalty. Any player who tests positive must go through treatment.

* A first-time positive test results in a 10-game suspension. A second positive results in a 25-game suspension. A third positive leads to a one-year playing ban. A player would be kicked out of the NBA for a fourth positive.

(Reporting by Deborah Charles, Editing by Jackie Frank)