CHARLOTTE, N.C. — An independent drug test on Jeremy Mayfield was negative for methamphetamines, contradicting the results of a NASCAR test taken 40 minutes earlier, the driver claimed in court documents filed Tuesday.

In response to NASCAR's claim that Mayfield again tested positive for methamphetamines on July 6, Mayfield submitted an affidavit to the U.S. District Court that said he traveled to Frye Regional Medical Center in Hickory, N.C., right after NASCAR collected a sample at his Catawba County home.

In a room he described as "very sterile," Mayfield said he emptied his pockets, washed his hands and was ushered into a bathroom, where he provided another urine sample.

Mayfield said in the court filing he received confirmation from Laboratory Corporation of America in Raleigh, N.C., that his sample was negative on July 10 — the same day NASCAR informed his counsel that its sample was positive.

He said the results of his test are "consistent with my lifestyle as I have not and do not use or abuse methamphetamines.

"It is impossible for methamphetamine to be in my body as I have never consumed that substance."

Dr. Harold Schueler of the Broward County (Fla.) Medical Examiner's Office, filed an affidavit on behalf of Mayfield that claimed the levels of methamphetamine in NASCAR's test are "astronomical" and "could not be remotely accurate, unless Mr. Mayfield was deceased or a chronic abuser."

The filing also denied accusations made last week by his estranged former stepmother, who said in her own affidavit she witnessed Mayfield use methamphetamines at least 30 times and that the driver cooked it himself until the ingredients became too hard to obtain. She also said she witnessed him use the drug at Darlington Raceway in 1999.

Mayfield was suspended May 9 for failing a random drug test taken eight days earlier for what NASCAR has said was a positive test for methamphetamines. The driver sued, and a federal judge issued an injunction July 1 that lifted his suspension based on the argument that NASCAR's testing system is flawed.

NASCAR asked U.S. District Court Judge Graham Mullen last week to reverse the injunction based on new evidence — the failed July 6 test and Lisa Mayfield's sworn testimony.

Mayfield's attorneys Tuesday argued in their response that the July 6 test results — positive or negative — should not be taken into consideration because the case is about a failed May 1 test.

"This Court's preliminary injunction lifted a suspension for a drug test performed on May 1, 2009, the questionable circumstances surrounding which necessarily remain unchanged," they wrote.