To test the effects of tyrosine ingestion with or without carbohydrate supplementation on endurance performance, nine competitive cyclists cycled at 70% VO_2peak for 90 min under four different feeding conditions followed immediately by a time trial. At 30 min intervals, beginning 60 min prior to exercise, each subject consumed either 5 ml^.kg^-1 body weight of water sweetened with aspartame [placebo (PLA)], polydextrose (70 g^.L^-1) (CHO), L-tyrosine (25 mg^.kg^-1 bw) (TYR), or polydextrose (70 g^.L^-1) and L-tyrosine (25 mg^.kg^-1 bw) (CHO+TYR). The experimental trials were given in random order and carried out using a counterbalanced double blind design. No differences were found between treatments for oxygen uptake (VO₂), heart rate (HR) or rating of perceived exertion (RPE) at any time during the 90 min ride. Plasma tyrosine rose significantly from PRE60 to test termination (TT) in TYR (means ± SE) (480 ± 26 µmol) and CHO+TYR (463 ± 34 µmol) and was significantly higher in these groups from PRE30 to TT versus CHO (90 ± 3 µmol) and PLA (111 ± 7 µmol) (p<0.05). Plasma free tryptophan was higher at E90, ETT15, and TT in TYR (10.1 ± 0.9, 10.4 ± 0.8, and 12.0 ± 0.9 µmol, respectively) and PLA (9.7 ± 0.5, 10.0 ± 0.3, and 11.7 ± 0.5 µmol, respectively) versus CHO (7.8 ± 0.5, 8.6 ± 0.5, and 9.3 ± 0.6 µmol, respectively) and CHO+TYR (7.8 ± 0.5, 8.5 ± 0.5, 9.4 ± 0.5 µmol, respectively) (p<0.05). The plasma tyrosine/free tryptophan ratio was significantly higher in TYR and CHO+TYR versus CHO and PLA from 30 min prior to exercise to test termination (p<0.05). CHO (27.1 ± 0.9 min) and CHO+TYR (26.1 ± 1.1 min) treatments resulted in a reduced time to complete the endurance time trial compared to PLA (34.4 ± 2.9 min) and TYR (32.6 ± 3.0 min) (p<0.05). These findings demonstrate that tyrosine ingestion did not enhance performance during a cycling time trial following 90 minutes of steady state exercise.