This study examined the effect of pre-exercise carbohydrate intake on blood glucose, blood lactate, and performance in competitive swimmers during sprint interval swimming. Ten male and 11 female swimmers performed two 4 × 50-m maximal sprint trials in their specialized stroke, spaced two days apart, in a random, counterbalanced order. In one trial (carbohydrate trial), the participants consumed a candy providing 1 g carbohydrates per kg body weight one hour before exercise, while, in the other trial (no-carbohydrate trial), they did not eat the candy. Blood glucose and lactate were measured before, immediately after, and 30 min after exercise. Performance time for each 50 m was recorded.