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The effects of varying sodium (Na) and carbohydrate (CHO) in oral rehydration solutions (ORS) and sports drinks (SD) for rehydration following exercise are unclear. We compared an ORS and SD for the percent of fluid retained (%FR) following exercise-induced dehydration and hypothesized a more complete rehydration for the ORS (45 mmol Na/L and 2.5% CHO) and that the %FR for the ORS and SD (18 mmol Na/L and 6% CHO) would exceed the water placebo (W). A placebo-controlled, randomized, double-blind clinical trial was conducted. To induce 2.6% body mass loss (BML, p > 0.05 between treatments), 26 athletes performed three 90 min interval training sessions without drinking fluids. Post-exercise, participants replaced 100% of BML and were observed for 3.5 h for the %FR. Mean ± SD for the %FR at 3.5 h was 58.1 ± 12.6% (W), 73.9 ± 10.9% (SD), and 76.9 ± 8.0% (ORS). The %FR for the ORS and SD were similar and greater than the W ( p < 0.05 ANOVA and Tukey HSD). Two-way ANOVA revealed a significant interaction with the ORS having greater suppression of urine production in the first 60 min vs. W (SD did not differ from W). By 3.5 h, the ORS and SD promoted greater rehydration than did W, but the pattern of rehydration early in recovery favored the ORS.