PURPOSE: To investigate the effect of ice slurry ingestion on thermoregulatory responses and sub-maximal running time in the heat. METHODS:: On two separate occasions, in a counterbalanced order, ten males ingested 7.5 g.kg of either ice slurry (-1 degrees C) or cold water (4 degrees C) before running to exhaustion at their first ventilatory threshold in a hot environment (34.0 +/- 0.2 degrees C, 54.9 +/- 5.9% RH). Rectal and skin temperatures, heart rate, sweating rate, and ratings of thermal sensation and perceived exertion were measured. RESULTS:: Running time was longer (P = 0.001) after ice slurry (50.2 +/- 8.5 min) versus cold water (40.7 +/- 7.2 min) ingestion. Prior to running, rectal temperature dropped 0.66 +/- 0.14 degrees C following ice slurry ingestion compared to 0.25 +/- 0.09 degrees C (P = 0.001) with cold water, and remained lower for the first 30 min of exercise. At exhaustion however, rectal temperature was higher (P = 0.001) with ice slurry (39.36 +/- 0.41 degrees C) versus cold water ingestion (39.05 +/- 0.37 degrees C). During exercise, mean skin temperature was similar between conditions (P = 0.992), as was heart rate (P = 0.122) and sweat rate (P = 0.242). Following ice slurry ingestion, subjects stored more heat during exercise (100.10 +/- 25.00 vs. 78.93 +/- 20.52 W.m; P = 0.005), and mean ratings of thermal sensation (P = 0.001) and perceived exertion (P = 0.022) were lower.