Glycerol-induced hyperhydration has been applied to endurance sport with limited success as a performance enhancement strategy. Glycerol has been used as a hyperhydrating agent, because it has been shown to be rapidly absorbed and osmotically active; therefore, the fluid intake with glycerol is distributed throughout the body. Hyperhydration with glycerol increases fluid retention compared to water alone, thus shown to be performance enhancing in hot conditions in which high fluid losses are likely. However, glycerol-induced hyperhydration studies limited to hot conditions may not be applicable to multisport events held in ambient temperatures. The aim of this study was to determine whether glycerol hyperhydration would improve performance in a long, simulated multisport time-trial (kayak, cycle, and run) under cool, ambient temperatures more so than hyperhydration with water alone. (Contains 3 tables and 1 figure.)