Exercise performance in the heat is not limited by the availability of carbohydrate (CHO), and the provision of more dilute CHO-electrolyte solutions may confer a greater benefit during prolonged exercise in a warm environment. The present study evaluated the effects of low concentrations of CHO on physical and mental performance. Twelve healthy males (mean±SD Age 21±2 years; Height 179±8 cm; Mass 80.2±7.1 kg; VO2max 4.2±0.5 l/min) exercised to volitional exhaustion at a workload corresponding to 60% VO2max at 30°C, 60% RH. Subjects ingested 3 ml/kg body mass of a 0%, 2%, 4% or 6% CHO solution before exercise and a further 1.5 ml/kg body mass of the appropriate solution every 10 min during exercise. Heart rate, core temperature, RPE and perceived thermal stress were recorded at regular intervals. Expired gas samples were collected to determine rates of substrate utilisation. Cognitive function was assessed using a computerised test battery. Exercise time to exhaustion was 94.5±24.5 min, 104.1±20.1 min, 105.5±26.7 min and 112.0±28.7 min in the 0%, 2%, 4% and 6% trials respectively (P=0.046). Drink CHO content did not influence heart rate (P=0.464) or core temperature (P=0.516). Rates of CHO (P=0.105) and fat (P=0.339) oxidation were not influenced by the drink ingested. The exercise bout resulted in a slowing of response times to a visual search task in the 0% and 2% trials (p<0.05). The present data demonstrate a positive relationship between drink CHO content and exercise time to exhaustion. There was some suggestion that CHO may attenuate decrements in motor skills tasks performed after exhausting exercise. The study was carried out in relation to the product Powerade and was funded in part by The Coca-Cola Company.