Mucosal immunity provides initial defence against upper respiratory tract infections (URTI). Recent literature suggests that salivary secretory immunoglobulin–A (S-IgA) could be used to help indicate an athlete’s risk of URTI. Football, a physically demanding intermittent sport often played in hot environments, has shown to place strain on the salivary immune system during heavy competition periods. Performing exercise in hot conditions can result in reductions in salivary S-IgA concentrations and provides a further stress on immune response. Pre-cooling an athlete prior to exercise reduces the level of stress, and helps delay fatigue. The effect pre-cooling prior to exercise in heat has on mucosal immunity is currently unknown. The purpose of this study was to determine the effect pre-cooling ice slurry ingestion had on mucosal immunity and intermittent exercise performance in hot environments. In a randomised crossover design, 8 semi-professional football players completed two trials of the intermittent soccer performance test (ISPT) in a heat chamber, set to 30°C and 50% relative humidity. Participants consumed, at a standardised rate, 7.5g·kg-1 of ice slurry beverage or control fluid, with a further 2g·kg-1 provided at half-time. Unstimulated whole saliva samples were collected at baseline, pre-exercise, half-time, post-exercise, and 1 h post-exercise. Ice slurry ingestion significantly lowered core temperature prior to exercise and showed a possibly beneficial effect in end of exercise core temperature, perceived comfort and exertion scores, mean sprint speed, and distance covered in the last 15 min of exercise. Ice slurry ingestion showed possibly harmful effects on salivary S-IgA concentration and secretion rate prior to exercise. The salivary S-IgA concentration and secretion rate decreases were short lived as post-exercise values returned to baseline levels. Ice slurry ingestion may cause a transient drop in salivary immune response after consumption which as sport scientists is important to note, however, it doesn’t appear to influence S-IgA following exercise when the open window period is most apparent. In conclusion, the findings of this thesis show that ingestion of ice slurry may be beneficial for intermittent performance, and aid an athlete’s perceived difficultly and thermal comfort. Ice slurry ingestion does not influence post-exercise salivary immune response, however, provides an effective method of pre-cooling an athlete prior to exercise without impairing performance or inducing gastric discomfort.