World Anti-Doping Agency chairman Dick Pound wants to investigate why Marion Jones' backup sample came up negative, clearing her of a positive doping test.

The B sample from the 30-year-old sprinter did not detect the banned endurance enhancer EPO, her lawyers said Wednesday. That means her initial positive result is thrown out. She was tested after winning the 100 metres at the U.S. track and field championships on June 23.

Pound said he found the inconsistent tests ``disturbing.''

``We are going to see how that happened, learn from it, and try to make sure it doesn't happen in the future,'' Pound, a Montreal lawyer, told BBC Radio on Sunday. ``The worry we have is that someone is misinterpreting things or doing things wrong.

``I suppose if our experts look at it and say on the basis of what we have seen there is no question it should have been positive, we have an opportunity to put that into play.''

One of Jones' lawyers, Howard Jacobs, criticized Pound's remarks.

``From what I have heard from our experts ... it was borderline positive to start with, so although it is very unusual, I cannot say I was shocked by it,'' Jacobs told the same BBC program. ``I would assume if the B was negative, you have to assume that the A was the mistake. Marion is very clear she has never taken performance-enhancing drugs and I think people should accept that.''

Jones dominated athletics in the late 1990s. At the Sydney Games, she became the first woman to win five Olympic medals _ taking gold in the 100, 200 and 1,600 relay, and bronze in the long jump and 400 relay.

Since then, her reputation has suffered. She is one of several athletes who testified to the federal grand jury investigating the Bay Area Laboratory Co-operative. Her ex-husband, C.J. Hunter, and BALCO founder Victor Conte have accused her of using banned substances, allegations she has denied.