NEW YORK (CNN) -- Releasing a report that links some of baseball's best to the use of performance-enhancing substances, former Sen. George Mitchell said Thursday it is critical that Major League Baseball restore the integrity of the game.
Former Sen. George Mitchell gives his report Thursday on steroid use in baseball.
"This is a serious problem that cannot be solved by anything less than a well-conceived, well-executed and cooperative effort by everyone involved in baseball," Mitchell said in announcing his findings.
"Everyone involved in baseball over the past two decades -- commissioners, club officials, the Players Association, the players -- shares, to some extent, in the responsibility for the steroid era," he said.
"There was a collective failure to recognize the problem as it emerged and to deal with it early on." Watch Mitchell report on steroid use in baseball »
Dozens of current and former major league baseball players, including Roger Clemens, Yankee teammate Andy Pettitte, sluggers Mo Vaughn and Gary Sheffield, and reliever Eric Gagne, are named as being linked to steroid use in the report. See players named on the list »
It's "a call to action, and I will act," Major League Baseball Commissioner Bud Selig said Thursday afternoon.
Selig announced he would take steps including embracing the recommendations contained in Mitchell's report and implementing as many as possible; dealing with the players named in the report; and reviewing comments about club personnel.
"Discipline of players and others identified in this report will be determined on a case-by-case basis. If warranted, those decisions will be made swiftly," Selig said. Watch Selig's reaction »
Several teams, contacted by CNN, said they were reviewing the report and would have no immediate comment.
A few others expressed their support for the report and for eliminating the use of banned substances from baseball.
But the head of the Major League Baseball Players Association had some critical words.
"Many players are named. Their reputations have been adversely affected, probably forever, even if it turns out down the road that they should not have been," Donald Fehr said.
Sources : The Mitchell Institute, DLA Piper, Bowdoin College, Biographical Directory of the U.S. Congress
Mitchell, Selig and Fehr will be asked to testify Tuesday at a House Oversight and Government Reform Committee hearing.
But lawmakers are already weighing in on the report.
"As a fan and former player, this is the saddest day in my life for baseball," said Sen. Jim Bunning, R-Kentucky, a nine-time All Star pitcher for the Detroit Tigers and Philadelphia Phillies.
He said the report was "a job well done," but contained one glaring hole: How to handle the records of players who used steroids.
"I believe that those players who tried to gain an unfair advantage by using these substances should have their records stripped," Bunning said.
The report describes how Clemens got injections of the steroid Winstrol in Clemens' apartment in Toronto's Skydome in 1998, according to Brian McNamee, named in the report as a possible distributor of steroids.
McNamee "injected Clemens approximately four times in the buttocks over a several week period with needles that Clemens provided," the report states.
"During this period of improved performance, Clemens told McNamee that the steroids 'had a pretty good effect' on him," the report says. Learn more about anabolic steroids »
McNamee injected Clemens with testosterone and human growth hormone after Clemens moved to the New York Yankees in 2000, the report says.
Clemens' attorney said the seven-time Cy Young Award winner "vehemently denies" the allegations in the report. Watch the attorney say Clemens is upset »
McNamee also became Pettitte's personal trainer in 1999, the report says.
"McNamee recalled that he injected Pettitte with human growth hormone ... on two to four occasions" in 2002 to help Pettitte recover from elbow tendonitis, the report says.
Mitchell embarked on his multimillion-dollar task at Selig's behest, who felt an inquiry was necessary after reading "Game of Shadows."
The book was written by two San Francisco newspaper reporters who chronicled the alleged drug use of home-run king Barry Bonds.
Bonds, who faces federal perjury and obstruction charges for allegedly lying in 2003 about his steroid use, set the record for career home runs this year -- 762. He hit 73 home runs in 2001 to top Mark McGwire's 1998 record. Before the McGwire-Sammy Sosa race -- which McGwire won with 70 homers to Sosa's 66 -- Roger Maris' record of 61 home runs in a season had stood for 37 years.
Mitchell's report references the 1998 home run duel, but only briefly mentions Sosa.
No one interviewed repeated former slugger and admitted steroid user Jose Canseco's charges that McGwire also was a steroid user, Mitchell said in the report. Watch Canseco say the report backs his claims »
He suggested, however, that the discovery of the steroid precursor androstenedione in McGwire's locker was a watershed moment for baseball in terms of it finally opening eyes to steroid use.
No other McGwire steroid connection is mentioned in the report, although Mitchell notes that he, too, refused to meet with investigators.
Mitchell's investigation was a difficult one because he had no subpoena power, meaning he had no way to force players or witnesses to cooperate with his investigation.
A major source for Mitchell's probe was Kirk Radomski, a former clubhouse employee for the New York Mets who is named in the report as a "significant source of illegal performance-enhancing substances until late 2005."
Radomski assisted with the report as part of his plea bargain with the federal government in the case against the Bay Area Co-Operative Laboratory; he pleaded guilty in April to illegally distributing performance-enhancing drugs.
Baseball didn't begin testing for steroids until 2003. In a CNN interview, Victor Conte, the founder of the Bay Area Co-Operative, said pro baseball's drug-testing policy is a farce.
Conte said the World Anti-Doping Agency lists 60 stimulants as banned substances, only half of which are recognized by Major League Baseball. By not including the other 30 substances on the list, baseball is essentially promoting their use, he said. Watch Conte explain why tougher testing is needed »
CNN's Steve Robinson and Alanne Orjoux contributed to this report.
All About Major League Baseball