"As difficult as it is, I will be returning it to the International Olympic Committee because I don't want it," Johnson wrote in a column in Tuesday's Daily Telegraph. "I feel cheated, betrayed and let down."

Pettigrew testified on May 22 at the trial of disgraced athletics coach Trevor Graham in San Francisco that he had used banned performance enhancing drugs throughout his long career. The testimony had been described earlier in the trial.

"The news that Antonio was scheduled to testify to having taken performance-enhancing drugs shocked me like no other drug-related story," Johnson wrote. "...He was someone I considered a friend."

The gold medal is one of five Johnson won in his standout career.

He still holds the world record in the 200 and 400 meters.

Pettigrew's testimony means that three of the four runners in the finals on the U.S. relay team have been tainted by doping.

Twins Alvin and Calvin Harrison both were suspended for doping violations. Alvin Harrison accepted a four-year ban in 2004 after admitting he used performance enhancers. Calvin Harrison tested positive for a banned stimulant in 2003 and was suspended for two years. Like Pettigrew, they were coached by Graham.

Earlier, Johnson had refused to give up the medal after it was revealed that another U.S. relay teammate, Jerome Young, had tested positive in 1999. Young, it was later ruled by the Court of Arbitration for Sport, had been wrongly cleared by U.S. officials to compete. He ran only in a preliminary round, and the athletes won an appeal to keep the medals.

During the Young controversy, Johnson wrote, he had spoken with Pettigrew and both agreed they should fight giving up the medal.

"I look back on those conversations now and am amazed that he could talk to me about this knowing all along that he was guilty and that the medal was tainted anyway," Johnson wrote.

Johnson said he is "deeply disappointed in Antonio and in the sport of athletics. I now realize that there have been a significant number of athletes and coaches in this sport who have cheated and taken the short cut, and many of them knew who else was cheating."

Johnson talked about his past rigorous defence of the sport against a media that he felt overemphasized doping and virtually ignored the true accomplishments of the athletes.

"But now," he wrote, "I feel that I have been naive."