Cognitive and mood decrements resulting from mild dehydration and glucose consumption were studied. Men and women (total N = 54; M age = 19.8 yr., SD = 1.2) were recruited from college athletic teams. Euhydration or dehydration was achieved by athletes completing team practices with or without water replacement. Dehydration was associated with higher thirst and negative mood ratings as well as better Digit Span performance. Participants showed better Vigilance Attention with euhydration. Hydration status and athlete's sex interacted with performance on Choice Reaction Time and Vigilance Attention. In a second study, half of the athletes received glucose prior to cognitive testing. Results for negative mood and thirst ratings were similar, but for cognitive performance the results were mixed. Effects of glucose on cognition were independent of dehydration.