His name appears on a list of 104 players who tested positive for performance-enhancing drugs in a 2003 baseball survey, SI said. He reportedly tested positive for Primobolan and testosterone while playing for the Rangers.
Rodriguez declined to discuss the tests when approached by SI on Thursday at a gym in Miami, where he lives in the offseason.
"You'll have to talk to the union," he told a reporter. Calls from SI to union head Donald Fehr were not returned.
Major League Baseball said it was "disturbed" by the report, but did not elaborate because of player confidentiality.
"Because the survey testing that took place in 2003 was intended to be nondisciplinary and anonymous, we cannot make any comment on the accuracy of this report as it pertains to the player named," MLB executive vice president Rob Manfred said.
The players' union refused to directly address the story's accuracy.
"Information and documents relating to the results of the 2003 MLB testing program are both confidential and under seal by court orders," the union said.
"Anyone with knowledge of such documents who discloses their contents may be in violation of those court orders," the union added.
An e-mail from The Associated Press to Rodriguez's agent, Scott Boras, was not immediately returned. The Yankees and Rangers had no comment.
In a December 2007 interview with "60 Minutes," three days after George Mitchell's report on drugs in the sport was released, Rodriguez denied using peformance-enhancing drugs.
"I've never felt overmatched on the baseball field. ... I felt that if I did my, my work as I've done since I was, you know, a rookie back in Seattle, I didn't have a problem competing at any level," he said.
Rodriguez played for the Rangers in 2003, when he won the AL home run title and MVP award. He was traded to the Yankees in 2004. He is drawing a major league-high $27 million salary after signing a record $275 million, 10-year contract with New York in 2007.
The revelations come at a time when baseball's focus on drugs has concerned Barry Bonds and the legal maneuvering leading to the start of his trial March 2. The government is trying to prove the home run king lied when he told a grand jury he never knowingly took performance-enhancing drugs.
Rodriguez until now has had an offseason dominated by talk of disclosures in Joe Torre's recently released book. The former Yankee manager wrote of the pressure A-Rod puts on himself and the third baseman's need to command the stage. Torre said some in the Yankees clubhouse referred to Rodriguez as "A-Fraud," although Torre made light of that during interviews promoting his book, "The Yankee Years."
Baseball's drug policy prohibited the use of steroids without a valid prescription since 1991, but there were no penalties for a positive test in 2003.
As part of an agreement with the players' union, the testing in 2003 was conducted to determine if it was necessary to impose mandatory random drug testing across the major leagues in 2004.
The results of the testing of 1,198 players were meant to be anonymous under the agreement between the commissioner's office and the union. SI reported that Rodriguez's testing information was found after federal agents, with search warrants, seized the 2003 results from Comprehensive Drug Testing, Inc., in Long Beach, Calif.
That was one of two labs used by baseball in connection with the testing. The seizure in April 2004 was part of the government's investigation into 10 baseball players linked to the BALCO scandal, the magazine reported. Rodriguez has not been connected to BALCO.
Primobolan, also known as methenolone, is an injected or orally administered drug. It improves strength and maintains lean muscle with minimal bulk development and few side effects. Bonds tested positive three times for methenolone, according to court documents unsealed by a federal judge Wednesday.
Primobolan is not an approved prescription drug in the United States. Testosterone can be taken legally with a prescription.
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