A day after learning Jeremy Mayfield failed a drug test for something other than a performance-enhancer, NASCAR allowed him to drive a race car at Darlington Raceway in South Carolina at speeds up to 173 mph.

A person familiar with the test results said yesterday that Mayfield's positive test was not for a performance-enhancing drug. NASCAR won't reveal what banned substance was found in the random test, which ultimately resulted in Mayfield's indefinite suspension.

NASCAR officials previously announced the drug violation was not alcohol-related, and the administrator of its drug testing program has dismissed Mayfield's explanation that the positive result came from a mix of a prescription with an over-the-counter medicine.

Under the sport's toughened policy, that leaves the possibility that Mayfield tested positive for abuse of a prescription drug, narcotics or controlled substances, such as cocaine, marijuana or methamphetamine.

Because Mayfield challenged the initial positive finding, as allowed under NASCAR's drug policy, the series did not take disciplinary action until his backup "B" sample also tested positive. That's why Mayfield wasn't barred from participating in two practice sessions and qualifying session May 8 at Darlington.

One of the former owners of Kentucky Motor Speedway says he won't be forced into dropping an antitrust lawsuit against NASCAR by new track owner Bruton Smith. Richard Duchossios said he's not sure why Smith has decided to go public with claims that the former owners have a "moral obligation" to race fans in Kentucky to drop the four-year-old lawsuit against NASCAR and International Speedway Corp.

Smith purchased the track last year for $78.3 million after the original ownership group tried unsuccessfully for almost a decade to land a coveted Sprint Cup race. Smith, towner of Speedway Motorsports Inc., is in the process of giving the venue a $70 million face-lift with the goal of finally bringing a Cup race to the area. Kentucky is the eighth NASCAR-sanctioned track in SMI's portfolio, but the only one without a Cup date.

SMI recently asked NASCAR to consider Kentucky for the 2010 Cup schedule, but the sanctioning body will not act on any proposals until the former owners drop their antitrust lawsuit against NASCAR and ISC, its sister company.

Spaniard Oriol Servia was the fastest of 10 drivers in practice hoping to qualify for the Indianapolis 500. Servia's fast lap of 221.343 mph was seventh overall in the six-hour practice session at Indianapolis Motor Speedway, where most of the 22 drivers already qualified for the May 24 race shared track time with the drivers trying to find enough speed to make it into the 33-car field in time trials tomorrow and Sunday.

Servia, who finished 11th a year ago as a rookie, completed 73 laps in his first appearance on the 2.5-mile Indy oval this season.

Next among the non-qualified drivers was Townsend Bell, who got his ride with KV late last week. He posted a lap of 220.938.