NASCAR is sticking to its policy of not disclosing the specific substances that cause positive drug tests.

Series President Mike Helton said Thursday that even though the rulebook allows series officials to disclose which drugs a competitor has tested positive for, he does not intend to stray from the long-standing policy of keeping those results private. Helton cited federal privacy laws as one reason the series has not publicly said what caused A.J. Allmendinger's positive test.

"A lot of it has to do with complexities of the whole process itself and realizing that you're dealing with personnel and personalities," Helton told a group of reporters. "We've chosen so far, anyway, to not disclose that. If the member wants to, that's their privilege to."

The comments come less than three weeks after Allmendinger tested positive for a banned substance at Daytona.

NASCAR has not provided details of the test and has said only that the two urine samples tested positive for the same substance. Allmendinger was suspended hours before the July 7 race and is now serving an indefinite suspension after his backup "B" sample also tested positive this week.

Allmendinger's business manager, Tara Ragan, said the driver tested positive for an amphetamine. Allmendinger has said he did not knowingly ingest a banned substance, and has hired an independent laboratory in an attempt to figure out how he tested positive.

But Allmendinger is not fighting the suspension and has instead said he will participate in NASCAR's anti-drug program, which includes an evaluation by a substance abuse professional, along with potential counseling and rehabilitation, so he can be reinstated.

Sam Hornish Jr. has replaced Allmendinger in Penske Racing's No. 22 car and will again this weekend. Hornish won the 2006 Indianapolis 500 on the historic 2.5-mile oval with a spectacular pass of Marco Andretti in the closing yards.

But as practice began for this weekend's Nationwide race in Indy, Allmendinger's test results and NASCAR's non-disclosure policy continued to be a major issue.

Helton didn't budge.

"We've just taken the position that we're not going to disclose," he said.

Helton added that the lack of positive drug-test results through the years, despite thousands of tests, indicated NASCAR's drug-testing policy did work.

"We take our responsibility very seriously," he said. "The fact it is (rare) is a very good thing for the sport."