This study examined whether a carbohydrate + casein hydrolysate (CHO+ProH) beverage improved time-trial performance vs. a CHO beverage delivering approximately 60 g CHO/hr. Markers of muscle disruption and recovery were also assessed. Thirteen male cyclists (VO2peak = 60.8 +/- 1.6 ml . kg-1 . min-1) completed 2 computer-simulated 60-km time trials consisting of 3 laps of a 20-km course concluding with a 5-km climb (approximately 5% grade). Participants consumed 200 ml of CHO (6%) or CHO+ProH beverage (6% + 1.8% protein hydrolysate) every 5 km and 500 ml of beverage immediately postexercise. Beverage treatments were administered using a randomly counterbalanced, double-blind design. Plasma creatine phosphokinase (CK) and muscle-soreness ratings were assessed immediately before and 24 hr after cycling. Mean 60-km times were 134.4 +/- 4.6 and 135.0 +/- 4.0 min for CHO+ProH and CHO beverages, respectively. All time differences between treatments occurred during the final lap, with protein hydrolysate ingestion explaining a significant (p < .05) proportion of between-trials differences over the final 20 km (44.3 +/- 1.6, 45.0 +/- 1.6 min) and final 5 km (16.5 +/- 0.6, 16.9 +/- 0.6 min). Plasma CK levels and muscle-soreness ratings increased significantly after the CHO trial (161 +/- 53, 399 +/- 175 U/L; 15.8 +/- 5.1, 37.6 +/- 5.7 mm) but not the CHO+ProH trial (115 +/- 21, 262 +/- 88 U/L; 20.9 +/- 5.3, 32.2 +/- 7.1 mm). Late-exercise time-trial performance was enhanced with CHO+ProH beverage ingestion compared with a beverage containing CHO provided at maximal exogenous oxidation rates during exercise. CHO+ProH ingestion also prevented increases in plasma CK and muscle soreness after exercise.