The adulteration of drug testing samples has been an ongoing problem in sport for many years and has become a commonplace in US firms which perform regular tests on employees. There are websites devoted to the issue of how to adulterate a sample for commercial testers.

International laboratories are a different matter to company screenings, however, and the paraphenalia is by necessity more exotic.

The dilution of urine, the concealment of bags of urine, the use of catheters and the abuse of injection oriented devices to fill bladders have all been used to keep ahead of the testers. Nor are the presence of strange substances in urine samples anything novel. Athletes have been known to slip vinegar, cleaning fluid, washing up liquid and a range of other substances into their samples to adulterate its quality.

The question for FINA and Michelle de Bruin will be to decide just when and how the substance emitting a "whiskey odour" entered the sample taken from the swimmer and to establish whether her B sample contains the same characteristics or shows any evidence of tampering.

Best known of previous cases is the instance of sprinter Katrin Krabbe and compatriots Silke Mueller and Grit Breuer who, having been randomly tested in South Africa in January 1992, submitted three identical samples of urine (believed to have come from a male).

They escaped punishment on a technicality, their federation not having had the powers to test randomly outside of their own country.

The German track and field federation also revealed at the time, however, that it suspected that Krabbe and Breuer had used the technique before in July 1991 because two samples provided by the athletes at that time were also from one individual, according to the results of lab analysis.

In 1978, the Belgian cyclist Michel Pollentier was stripped of first place in the Tour de France when he was apprehended in doping control with a rubber bag strapped to his armpit and filled with clean urine out of which came a tube which disappeared southwards.

Weight-lifting and body building report cases of female competitors filling their own bladders with uncontaminated urine or inserting dissolvable capsules of adulterating substance inside themselves the content of which they will expel at the right moment. Athletes of both sexes have been known to use catheters to influence the outcome of tests.

Challenging the science of drug tests is a difficult business as the burden of proof lies with the accused. Diane Modahl, Sandra Gasser of Switzerland, Angel Meyers (the US swimmer) and Butch Reynolds are the only people to have gone to court to challenge the science of drug tests. The Reynold's case perhaps pertains more precisely to the Michelle de Bruin saga than the much quoted Diane Modahl case, as the Reynold's case hinged, as does de Bruin's, on questions regarding the chain of custody. Dr David Black, testifying on behalf of Reynolds, raised doubts about the security of the Envopak system that contains the urine samples, demonstrating that it could be picked with a dental pick.

This did not prove that the Reynolds sample had been tampered with but created some doubt about the system. The bottles inside the Envopak, however, were then as now marked with a code number, sealed with a tab that has a coded number on it. No breach of this stage of the testing process has been reported and the bags have since been redesigned.

Other cases have revolved around procedural issues also. An American discus thrower John Powell was informed in 1987 that a sample of his had tested positive for the steroid nandrolone but due to a labelling error, the American track and field authorities could not legally prove that the sample concerned was actually his. Previously two American athletes August Wolf and Billy Olsen had succesfully challenged their federation over the validity of testosterone testing.

Their victory brought about a change in the legal ratio. A ratio of testosterone:epitestosterone of 6:1 became the legal limit and it became the onus of the athlete to prove that a deviation from that sort of ratio was not as a result of drug use.