Stop sign for Mayfield

That dubious distinction belongs to Jeremy Mayfield.

NASCAR officials placed the 39-year-old driver and owner of the No. 41 Toyota on immediate and indefinite suspension last weekend after he failed a random drug test taken the week before at Richmond. According to the provisions of its zero-tolerance policy, which was implemented at the start of the 2009 season, NASCAR does not disclose the nature of the abused substances, nor does it have a list of banned substances. However, the Associated Press, citing a source with knowledge of Mayfield's test results, reported it was not a performance-enhancing drug.

"It's not relevant to the public interest," NASCAR spokesman Ramsey Poston told the AP. "What's relevant is that this guy failed the test. It's a zero-tolerance test. That's all that matters."

Mayfield, in a statement released last weekend at Darlington, S.C., claimed, "the combination of a prescribed medicine and an over-the-counter medicine reacted together and resulted in a positive drug test."

However, the physician who oversees NASCAR's drug-testing program dismissed that assertion.

"A combination of an over-the-counter drug taken with a prescription drug could not cause the positive that we took action on," said Dr. David Black, CEO of Aegis Sciences Corp., the Nashville-based company that handles NASCAR's testing program.

Mayfield was informed of his failed drug test May 5, four days after he was tested. He was asked to explain why he tested positive, in accordance with NASCAR procedures. After Aegis investigated and then rejected Mayfield's claim, NASCAR officials were notified last Wednesday of Mayfield's positive test.

When Mayfield arrived at Darlington, he was not subjected to further testing, but requested to have his "B" sample tested. NASCAR allowed the driver to take the track for practice and qualifying for last Saturday's Southern 500. He ran 16 laps in the first practice session, and 23 in the second, running a fast lap of 173.577 miles per hour. He ran two qualifying laps, but failed to make the 43-car field.

"Certainly we were in contact with Jeremy that day, and there was no physical reason to believe he couldn't perform," Poston said. "Dr. Black's team had a rush order to get us the results. They literally worked through the night so we would know the 'B' sample before [last] Saturday night's race."

When it, too, tested positive, NASCAR immediately suspended Mayfield.

Now the sanctioning body is facing questions about whether there should be more transparency in its program through the disclosure of its banned substances.

"I do feel that we would all feel a little bit better if we knew because when you pick up the paper and you see NASCAR zero tolerance, what does that mean?" said Mark Martin, winner of the Southern 500. "If you're taking something as prescribed, what does zero tolerance mean? So it's just a little bit scary. I'm sure that we're all overreacting a little bit but certainly nobody wants to be caught up in that."

NASCAR chairman Brian France termed Mayfield's transgression as "a serious violation of our test, our substance-abuse policy, which gets you an automatic and indefinite suspension," he said. "And that's where we stand with Jeremy. We've said it's serious."

It was serious enough for NASCAR to make an example of the first Sprint Cup driver to test its zero tolerance for drugs.

"A 10-lap shootout is a huge, huge deal," Martin said of the not-so-new wrinkle to this year's format. "It puts a lot of excitment in it, a sense of urgency. I think it's a good move. Sparks will fly once again at Lowe's Motor Speedway."

The All-Star Race (9 p.m., SPEED) will be preceded by the Sprint Showdown at 7, a 40-lap, 60-mile qualifier that will vault the top two finishers into the field for the All-Star race. Five drivers among the top 20 in the Sprint Cup standings will be vying for the right to advance: Juan Pablo Montoya (14th in the points), David Reutimann (15th), Brian Vickers (17th), Martin Truex Jr. (19th), and Marcos Ambrose (20th).

Jimmie Johnson earned the pole in qualifying last night, holding off Kurt Busch. Matt Kenseth will start third, followed by Dale Earnhardt Jr. and Martin.

Ryan Newman, who will be making his eighth start in the non-points race, recalled his triumph the 2002 All-Star race as his favorite moment.

"We raced our way into the race and then started last," Newman said. "We made the cut then got the invert and had a fast racecar, that was really cool because nobody expected us to even be in the race. When you race your way in, then beat the best, in my opinion that was a true All-Star moment."

After the team lost its primary sponsor, Ethanol, team co-owner Bobby Rahal, the 1986 Indy 500 winner, vowed his team would find a sponsor for Indy, and signed up DAFCA, a microchip security company, to a one-race deal.

Thursday, in his first day on the track, Servia showed he was up to speed, turning a fast lap of 221.353 m.p.h. He wound up seventh-fastest overall.

"When you are driving for Rahal Letterman, you better step on it," said Servia, who finished 11th in his Indy debut a year ago. "They won this race in 2004 [with Buddy Rice], and honestly, the car felt great the moment I stepped into it."

Michael Vega can be reached at vega@globe.com; material from wire services, various sanctioning bodies, race teams, sponsors and track publicity departments was used in the preparation of this report.