The aim of this study was to investigate fluid and electrolyte balance in elite Gaelic Football players (n=20) during a typical training session in a warm environment (16 to 18 degrees C, 82-88% humidity). Pre-training urine samples were used to determine hydration status. Sweat sodium concentration was collected from four body site locations using absorbent patches. The mean sweat rate per hour was 1.39 l x h(-1) and mean body mass loss was 1.1%. Mean sweat sodium concentrations were 35 mmol x l(-1) (range 19-52 mmol x l(-1)). On average, players did not drink enough fluid to match their sweat rates (p<0.001) and this fluid deficit was not related to pre-training hydration status (p= 0.67). A single hydration strategy based on published guidelines may not be suitable for an entire team due to variations in individual sweat rates. Maximising player performance could be better achieved by accurate quantification of individual fluid and electrolyte losses.