Creatine is an endogenous guanidine compound found in the skeletal muscles and plays an important role in the metabolism of proteins. A perusal of the information available on the Internet concerning creatine revealed that its activity receives a great deal of attention, with much speculation about its ability to increase lean body mass, high-intensity power output, and strength in humans. Many of the entries available on the World Wide Web come from vendors of creatine. However, creatine differs from many other dietary supplements because its use is advocated by many physicians for many indications. Clinical laboratory monitoring of creatine therapy is currently available and uses HPLC-UV. The plasma creatine concentration increases following oral administration of creatine supplement, and the degree of increase is related positively to the dosage. A method has been developed for the determination of creatine in dietary supplements by using ion pair chromatography (IPC) with UV detection. The objectives of this study were (1) to determine the content of creatine in over-the-counter (OTC) dietary supplements, and (2) to evaluate the stability of creatine in aqueous solutions during storage.