There is compelling evidence that some dietary supplements consumed by the general population are manufactured and stored under conditions that lead to contamination of the end product with small amounts of extraneous materials. In most cases, this is harmless, but for athletes liable to drug testing as a consequence of their participation in sport, the potential consequences of even trivial amounts of a prohibited substance may be catastrophic. Quality control procedures for pharmaceutical products normally specify the absence of contaminants at a level of more than 0.1%, ie 1mg/g. However, in the case of an anabolic steroid such as nandrolone, the amount that will cause a positive test has been estimated to be about 1-3µg (Geyer et al, 2004). In the case of a supplement that is taken in high doses (20-30 g/d), such as for example creatine, this means that a contamination level of something closer to 0.00001% (ie 1µg/g) may cause a positive test. This work have been supported by recent findings from our laboratory (Judkins et al, 2006). These data demonstrate that as little as 10μg of 19-noradrostenedione (19-NorAD) added to a creatine supplement resulted in a positive doping test in all volunteers testing. This is one thousand times less that the purity level specified for pharmaceutical agents and at this level, these contaminants are without any pharmacological action.