Sweat is produced during exercise to help dissipate some of the extra heat produced due to an increase in metabolic rate. Inadequate drink ingestion during exercise means athletes finish exercise hypohydrated and when the time between exercise bouts is short, effective rehydration strategies will be necessary to prevent subsequent performance impairment. For complete rehydration, drink volumen must be sufficient to replace sweat losses as well as the additional water losses during recovery. Once a sufficient volume of drink is ingested it is the drink composition that dictates the rehydration success of the drink. It is well known that addition of sodium and some other nutrients to rehydration drinks enhances fluid balance restoration after exercise, but the effects of milk proteins have been less well documented. Skimmed milk is an effective post-exercise rehydration solution and enhances the restoration of fluid balance after exercise-induced dehydration to a greater extent than a carbohydrate-electrolyte sports drink. Whilst there are a number of factors in skimmed milk that might be responsable for this enhancement of rehydration, it appears that some of the effect is due to the milk protein, as milk protein has been shown to be more effective for post-exercise rehydration than an isoenergetic amount of carbohydrate. Whilst the effects of whey protein on post-exercise rehydration are equivocal, whey protein addition to a carbohydrate-electrolyte rehydration solution certainly does not impair rehydration. Therefore, in situations where protein ingestion alter exercise might be advantageous for the athlete, this protein might also enhance restoration of fluid balance.