The aim of the present study was to evaluate possible modulatory effect of the treatment with L-lysine and L-arginine on neuroendocrine activation during psychosocial stress in healthy subjects with relatively high trait anxiety in a randomized, double blind placebo controlled trial. In 29 healthy subjects at the upper limit of the normal range of a trait anxiety scale, a mixture of L-lysine and L-arginine (3 g each/day) was administered for 10 days followed by exposure to a psychosocial stress procedure based on public speech. Hormone levels, cardiovascular activation and skin conductance were measured. Amino acid treatment resulted in enhanced adrenocorticotropic hormone, cortisol, adrenaline and noradrenaline levels and galvanic skin responses during stress compared to those in placebo-treated group. Increases in the heart rate and blood pressure in response to public speaking task were not influenced by amino acid treatment. Results of the present study support the hypothesis that L-lysine in combination with L-arginine, which may induce anxiolytic effects, modify hormonal responses during psychosocial stress in humans. Such action may represent a normalization of hormone levels to the pattern observed previously in subjects with low trait anxiety.