The effects of tyrosine on mood, performance, heart rate and blood pressure of 16 healthy young subjects were assessed. Subjects were tested on two separate days, one test session after ingestion of 100 mg/kg tyrosine and the other test session after placebo, in random order. While performing a number of stress sensitive tasks, subjects were exposed to a stressor consisting of 90 dB noise. Tyrosine was found to improve the performance on two cognitive tasks, which were performed 1 h after administration of the medication and which could be characterized as highly sensitive to stress. In addition, tyrosine decreased diastolic blood pressure 15 min after ingestion, while 1 h after ingestion diastolic blood pressure was the same with tyrosine and placebo. No effects on mood, systolic blood pressure and heart rate were found.