Studies of the dietary practices of athletes report that nutritional supplements are commonly used. Supplementation practices vary between sports and individual athletes; however, there is evidence that at least some athletes use a large number of supplements concurrently, often in doses that are very high in comparison with normal dietary intakes. In exploring supplementation practices we propose a classification system separating the supplements into dietary supplements and nutritional erogogenic aids. The dietary supplement is characterised as a product which can be used to address physiological or nutritional issues arising in sport. It may provide a convenient or practical means of consuming special nutrient requirements for exercise, or it may be used to prevent/reverse nutritional deficiencies that commonly occur among athletes. The basis of the dietary supplement is an understanding of nutritional requirements and physiological effects of exercise. When the supplement is used to successfully meet a physiological/nutritional goal arising in sport it may be demonstrated to improve sports performance. While there is some interest in refining the composition or formulation of some dietary supplements, the real interest belongs to the use or application of the supplement; i.e. educating athletes to understand and achieve their nutritional needs in a specific sports situation. The sports drink (carbohydrate-electrolyte replacement drink) is a well known example of a dietary supplement. Scientific attitudes towards the sports drink have changed over the past 20 years. Initial caution that carbohydrate-electrolyte fluids compromise gastric emptying during exercise has now been shown to be unjustified. Numerous studies have shown that 5 to 10% solutions of glucose, glucose polymers (maltodextrins) and other simple sugars all have suitable gastric emptying characteristics for the delivery of fluid and moderate amounts of carbohydrate substrate. The optimal concentration of electrolytes, particularly sodium, remains unknown. Most currently available sports drinks provide a low level of sodium (10 to 25 mmol/L) in recognition that sodium intake may promote intestinal absorption of fluid as well as assist in rehydration. The sodium level of commercial oral rehydration fluids (used in the clinical treatment of diarrhoea and dehydration) is higher than that of the present range of sports drinks. However, even if research indicates that intestinal glucose transport is optimally stimulated at higher sodium concentrations, concern for the palatability of sports drinks may impose a lower ceiling for sodium levels. Commercial viability of a sports drink requires that it provide a refreshing and palatable fluid replacement across a wide variety of sports and exercise situations.(ABSTRACT TRUNCATED AT 400 WORDS)