Batchelder, BC, Krause, BA, Seegmiller, JG, and Starkey, CA. Gastrointestinal temperature increases and hypohydration exists after collegiate men's ice hockey participation. J Strength Cond Res 24(1): 68-73, 2010-The cold environments in which ice hockey players participate are counterintuitive to the predisposing factors of heat- and hypohydration-related illnesses. This population has received little consideration in hypohydration-related illness risk assessments. Protective equipment, multiple clothing layers, and performance intensity may predispose these athletes to significant decreases in hydration and increases in core temperature. The purpose of this study was to measure hydration status and gastrointestinal temperature (TGI) in male ice hockey players during practice sessions that focused on preseason skill development and cardiovascular conditioning. The study used a repeated measures design. Data were collected in a collegiate ice hockey rink (ambient temperature = 6.03 ± 1.65° C; relative humidity = 40.4 ± 11.89%). Seventeen ice hockey players (age = 20.6 ± 1.1, height = 180 ± 5 cm, mass = 85.04 ± 7.9 kg) volunteered for this study. Urine-specific gravity (USG) and body weight were measured before and after two 110-minute practice sessions. Urine reagent strips measured USG. Calibrated CorTemp (HQ, Inc., Palmetto, FL, USA) radiofrequency telemetered thermometers collected TGI before, during, and after two 110-minute practice sessions. Individual participant sweat rates were calculated. Data from both sessions were pooled. TGI (p < 0.0001), and USG (p < 0.0001) increased over the 110-minute session. Post-exercise body weight (83.9 ± 7.6 kg) was statistically lower (p < 0.001) than the pre-exercise weight (85.0 ± 7.9 kg). Sweat rates were calculated to be 0.83 ± 0.50 L·h−1. These male ice hockey players become hypohydrated during participation potentially predisposing them to dehydration-related illnesses. This change in hydration status resulted in a gastrointestinal temperature increase and significant weight loss during activity. Prevention and rehydration strategies such as those developed by the American College of Sports Medicine and National Athletic Trainers' Association should be implemented to reduce the possibility of heat-related illness for this population.