LAUSANNE, Switzerland -- The IOC gave the go-ahead Thursday to retest drug samples from the Salt Lake City Olympics for the steroid THG.

The executive board approved the plan after determining there were no legal or scientific obstacles to rescreening frozen samples from the 2002 Winter Games.

"The IOC does not want to leave any stone unturned in the fight against doping," spokeswoman Giselle Davies said.

Patrick Schamasch, medical director of the International Olympic Committee, said it was not yet known how many of the 600 samples taken in Salt Lake City would be retested, or when the process would begin. The samples are stored at the Olympic doping control laboratory at UCLA.

IOC president Jacques Rogge said this week he doesn't expect any positives from the Salt Lake samples. He said THG appears to be limited to athletes connected with Bay Area Laboratory Co-Operative, the California company under investigation by a federal grand jury in San Francisco.

THG, or tetrahydrogestrinone, was unmasked this summer as a steroid chemically modified to avoid detection in standard tests. A test for THG was then developed at the UCLA lab.

At least five track and field athletes, including British sprinter Dwain Chambers and U.S. middle-distance runner Regina Jacobs and shot putter Kevin Toth, and four NFL players have tested positive for THG.

Track and field's governing body retested about 400 samples from the world championships in August in France and found two positive THG cases, both involving athletes with previous positive tests for the drug.

The International Swimming Federation said Wednesday that retesting of samples from last summer's world championships in Barcelona, Spain, turned up no positive findings.