To evaluate the immediate effect of exposure to a high level of noise on the sympatho-adrenal and pituitary-adrenal systems, measurements were made of circulating catecholamines, growth hormone, ACTH, and cortisol in seven normal male subjects. They were studied on two random experimental days: a control day and a noise-exposure day with an intermittent noise alternating between 99 dB (A) and 45 dB (A) for 2 h. Analysis did not reveal any variation in the plasma levels of norepinephrine (NE), epinephrine (E) or dopamine (D), measured every 20 min, which might have been related to noise exposure. Similarly, analysis of the 2-h urine samples collected from 8 a.m. to 2 p.m. revealed no significant changes in urinary catecholamine excretion. Plasma levels of GH and ACTH did not differ significantly from those for control days, but cortisol showed a brief, significant levelling-off in its pattern during the exposure period. The data demonstrate that exposure to a high level of noise, although considered as "unpleasant", does not induce any important endocrinological changes in man. These conclusions differ from those for studies on animals where reactions to noise may be related to a more general stressing situation.