Don Catlin did not detect anabolic steroids in the urine sample of a female athlete he analyzed last spring. Yet he believed they were present. The sample struck him as odd.

Catlin, the director of the UCLA Olympic Analytical Laboratory in Los Angeles, had examined the urine of athletes in Olympic sports for years. Though this one did not show evidence of any of the dozens of steroids Catlin had been trained to identify, the levels of several natural hormones in the sample were strikingly low, almost nil. Catlin knew that anabolic steroids tend to suppress a person's production of natural steroids. That fact alone strongly suggested that an anabolic steroid had been used.

But where was the steroid?

Catlin's curiosity led to the discovery of what drug-testing officials refer to as a designer steroid -- a drug that cannot be detected by standard drug tests -- and it set off a search for the producer of the drug that has homed in on the lab of a renowned U.S. chemist, raised questions about how long the drug may have been used to beat drug tests and attracted the interest of federal investigators.

A combination of research and detective work led Catlin and officials of the U.S. Anti-Doping Agency to the identification of an obscure but powerful steroid -- known as norbolethone -- in two samples of the athlete's urine after obtaining a sample of it from the chemical library of Wyeth Laboratories in Philadelphia. Wyeth studied norbolethone during the 1960s, as interest in the medical uses of synthetic steroids peaked, but it eventually abandoned the research and never marketed the drug. Norbolethone had never been found in an athlete's urine prior to Catlin's discovery.

"Discovering an unmarketed steroid last known to have been given to humans in a clinical trial 30 years ago raises an interesting question," Catlin wrote in the scientific paper on the discovery that appeared in Rapid Communications in Mass Spectrometry last May. "What is the source of this steroid today? It is quite unlikely that a supply of norbolethone remains from the few clinical studies conducted between 1964 and 1972. Thus, someone or some organization with synthetic chemical expertise could be preparing norbolethone."

U.S. Anti-Doping officials, who oversee Olympic drug-testing in the United States, say they believe there may be a connection between Patrick Arnold, who is considered the most prominent dietary supplement manufacturer in the United States, and norbolethone. They have turned over files to the U.S. Attorney's Office in the Central District of Illinois that indicate Arnold might have made the drug.

Arnold, of LPJ Research in Seymour, Ill., said during an interview last fall that he might have produced small quantities of norbolethone to satisfy his personal curiosity in the past, but he objected to any link between himself and the athlete who tested positive, cyclist Tammy Thomas of Yazoo City, Miss.

Thomas received a lifetime ban from USA Cycling because the test represented her second drug-testing violation in two years.

Arnold speculated that the norbolethone she is alleged to have used would likely have been a "custom-order thing" from a steroid manufacturer in China.

"Did I make norbolethone?" Arnold said. "I don't want to answer that question. I may have made a lot of things at one time. . . . I've made things for personal curiosity before, years in the past. . . . I'm not sure if that was one of them or not. There were certain compounds I was curious about. . . . I don't see why you are making the connection between that and this case [involving the cyclist].

"If you make a few hundred milligrams of a substance, it's not going to be enough to feed an athlete, or whatever. . . . Norbolethone's not a very obscure compound. If you look in the Merck index, it's there."

There appears to be no evidence linking Arnold and Thomas, who denied taking steroids and claimed the oddities in her urine samples were caused by emergency birth control.

Timothy Bass, an assistant U.S. attorney in the Central District of Illinois office, has begun looking into whether Arnold might have violated any laws through the production or distribution of steroids, The Post has learned. Bass declined to comment. Though anabolic steroids were banned by Congress in 1990, norbolethone is not considered illegal because it was barely known at the time and was not mentioned in the law. However, the Food and Drug Administration does not allow for the commercial distribution of drugs without its approval.

Public rumors of the use of norbolethone, also known as Genabol, circulated soon after the 2000 Sydney Olympics. Track coach Charlie Francis -- who coached Ben Johnson when he tested positive for steroids at the 1988 Summer Games in Seoul -- wrote about the steroid, referring to it as Genabol, in the Oct. 26, 2001, issue of Testosterone Magazine. Francis recently made headlines by working as a consultant for two months to sprinting stars Marion Jones and Tim Montgomery.

"Another unmodified drug that became widely used up to and during the Sydney Olympics was Genabol," Francis wrote. "This drug was brought to the attention of the drug testers in 1984, but as it wasn't in commercial production, a test wasn't developed for it. Once athletes became aware of this loophole, a market quickly developed for the drug. . . . By the time a test was developed, the word was out and the athletes moved on to other products."

Francis declined a request to expand on his comments in the article.

Ray Kazlauskas, who oversaw the drug-testing laboratory at the Olympics in Sydney, said it was not possible to reevaluate the urine samples taken from athletes at those Games to check for the presence of norbolethone. The samples themselves were not saved, he said.

Arnold is credited with being the first in the United States to make androstenedione, the legal steroid sold in over-the-counter supplements that soared in popularity when former major league baseball player Mark McGwire admitted using it in 1998. Arnold also invented 1-testosterone, a legal steroid considered more powerful than androstenedione that has revolutionized the dietary supplement market in the last year.

During her hearing in front of the American Arbitration Association, Thomas was asked if she knew Arnold, according to several sources. She said no.

Drug-testing officials have long suspected that designer drugs are used by top athletes in Olympic sports to beat drug tests. The discovery of norbolethone was considered a major coup for Catlin and the U.S. Anti-Doping Agency, as designer drugs are virtually never detected.

The find was actually the second breakthrough for Catlin in a period of months. During the Salt Lake City Olympics last February, Catlin found the previously undetected darbepoetin -- a substance similar to the endurance enhancing erythropoietin (EPO) -- in samples of several cross-country skiers. Less than 5 percent of athletes in Olympic sports test positive for banned drugs.

USADA chief Terry Madden said a variety of information led drug-testing officials to believe that Arnold may have at one time made norbolethone.

Because USADA's information, which came largely from secondhand sources and the Internet, seemed to be beyond USADA's scope, officials said, they passed it on to federal investigators.

"When we find something this unusual . . . a designer drug, our interest is both in terms of getting through the case as a doping violation and also what the source might be," said Larry Bowers, USADA's senior managing director. "We have very limited capability to do investigations."

Arnold is believed to be the only prominent dietary supplement manufacturer in the United States who makes all of his own compounds, a distinction for which he claims credit. Others design their products but usually place orders for materials from manufacturers in China or Europe.

Anabolic steroids were made illegal in the United States for non-medical purposes after Congress heard testimony in the late 1980s about their potential ill effects and widespread abuse in sports. Thomas, who was also suspended for a year in 2000 after a series of urine tests showed a high testosterone-to-epitestosterone ratio, told The Post last summer that she had never taken anabolic steroids.

Thomas, 33, had risen through the ranks of track cycling in the 1990s but became a polarizing figure within the sport after her first positive test, which came just as she was about to face Olympic medalist Chris Witty in a ride-off for an Olympic team slot. Many cyclists were angry that Thomas negotiated a one-year suspension with USA Cycling and the U.S. Olympic Committee; a two- or four-year suspension for athletes accused of taking anabolic steroids is customary.

Thomas, listed at 5 feet 7, 159 pounds, won a silver medal at the World Track Cycling Championships in Antwerp, Belgium, in 2001. A three-sport athlete in high school, she took up cycling after her graduation from Mississippi State University in 1992.

When Thomas's ban was announced last summer, many riders and cycling officials who were skeptical of her achievements celebrated the news.

"When I saw her last, it was very obvious to me and others that she had gained upper body weight," said Pat McDonough, a coach at the Lehigh Valley Velodrome in Allentown, Pa. "There were pronounced differences in her physical appearance. . . . Her voice is deep, there's definitely facial hair, it's one of those things. If you look at a checklist of side effects [of steroids] and you just keep going down the list, you check all the boxes. . . . It's a shame about her personally, but it's very important for our sport to win a few of these battles and send some messages to people."

Catlin found norbolethone in two of Thomas's urine samples -- from March 2002 and August 2001.

After the first scan of the sample aroused suspicions, Catlin called for a more detailed scan that produced an unexpected peak that Catlin could not account for. A closer look at the results revealed the presence of metabolites similar but not identical to those produced by a known steroid known as norethandrolone.

Catlin put the test aside -- it was, after all, technically negative -- but began thumbing through old steroid manuals and textbooks to see if he could find a substance that might have yielded such an unusual result. He quickly focused his attention on norbolethone, as it was a close relative of norethandrolone and seemed to have the properties that would appeal to athletes seeking to gain strength.

After researching the history of norbolethone, Catlin wrote a letter to Wyeth, requesting a reference standard of the old drug -- which was essential to identify positively the substance in the urine sample.

After receiving the sample about two months later, Catlin used a mass spectrometer to compare the peaks in Thomas's urine sample with those produced by norbolethone. The results showed a match. Norbolethone was the mystery substance.

Thomas argued unsuccessfully at her hearing last summer that her positive tests for norbolethone were caused by using the Plan B emergency contraception levonorgestrel, which is a synthetic progestogen that happens to be similar chemically to norbolethone.

Thomas testified that she engaged in unprotected sex the day before each sample was taken and used the emergency birth control on the day of the unannounced drug tests. She told The Post last summer she could not afford daily birth control pills. She described herself as "a poor athlete."

On her drug-test disclosure form, she disclosed several vitamins and substances she had used, but did not mention the birth control. She said at her hearing that she considered the use of such medication a private matter.

The arbitration panel acknowledged there was a "theoretical possibility" that the birth control drug could have converted in the body to norbolethone but the defense was viewed as "inadequate" to explain the positive tests. "Levonorgestrel is a known artificial steroid with readily available markers that are easily seen" in drug screens, the court stated in its Sept. 6 opinion.

Gorden Hughes, one of the leaders of the team of scientists at Wyeth that studied norbolethone 40 years ago, said he didn't know why the steroid was never marketed. "It wasn't dropped for reasons of being poisonous or ineffective," he said during a phone interview from his home in Haverford, Pa. Published research on the steroid suggest it would be useful to athletes as its anabolic activity (muscle-building effects) is said to exceed its androgenic activity (negative side effects) by a factor of 20.

William Llewellyn, the author of "Anabolics 2002: Anabolic Steroid Reference Manual," said Catlin's discovery of norbolethone did not suggest that drug-testing officials could routinely foil athletes who attempt to disguise their use of performance-enhancing substances.

Designer steroids are "something that, if you really know the right person, you can get your hands on," Llewellyn said. "It's like a big community in all of the sports. Athletes who are taking performance-enhancing drugs can slip through the testing. . . . It's a largely accepted fact of competition that you can take certain drugs to get an edge. The Olympics is not even close to drug free. People on the inside know the truth."

An irregular urine reading led Olympic drug lab analyst Don Catlin to discover a previously undetectable steroid.USA Cycling banned Tammy Thomas for life after 2nd drug test violation, which brought the designer steroid norbolethone to attention of analysts. William Llewellyn, author of a steroid reference manual, said despite norbolethone's discovery, drug testers will still chase behind athletes.