The "Beverage Hydration Index" (BHI) was created to assess the degree to which beverages "hydrate", by measuring fluid retention after ingesting a 1 liter bolus and comparing it to water. Drinks with carbohydrates and electrolytes would traditionally be expected to score higher on the BHI due to glucose-sodium cotransport at the gut and osmolality approaching isotonicity with blood. One recent study reported that an oral rehydration solution (ORS) scored better than water, but a "sports drink" did not. No "optimal" BHI beverage composition has been described, nor has an optimal osmolality. Recently, a hypotonic amino acid-based rehydration beverage was developed to take advantage of amino acid-sodium cotransport, thus obviating the need for carbohydrate. However, the BHI of this beverage has not yet been assessed. The purpose of this investigation was to assess the hydration potential of this novel beverage in comparison to a commercially available carbohydrate-containing sports drink and oral rehydration solution.