Some neuroendocrine parameters known as stress indices were examined in two groups of healthy male workers in a glass factory: the first group (60 subjects) was exposed to high environmental noise levels [greater than 90 dB(A)]; the second group (52 subjects) was exposed to low noise levels [less than 78 dB(A)]. Subjects with histories of cardiovascular diseases or high arterial pressure were excluded from the study. In both groups serum catecholamines and cortisol, and urinary vanilmandelic and homovanillic acids were evaluated at the beginning and middle of morning and afternoon work-shifts, by high performance liquid chromatography with electrochemical detection. Norepinephrine, epinephrine and vanilmandelic acid were significantly increased (P less than 0.01) during work-shifts in the group exposed to 90 dB(A), compared with baseline levels and also with catecholamine levels in the group exposed to 78 dB(A). Serum dopamine, cortisol and homovanillic acid showed no significant differences. The increased stimulation of the sympatho-adrenal system in response to high and prolonged noise exposure might lead to an abnormal response of the cardiovascular system with increasing arterial pressure values.