This quasiexperimental field study explored the effect of noise attenuation on urinary cortisol excretion (sampled three times, at 6:30 and 10:30 AM and 1:30 PM) and reported fatigue and postwork irritability among 35 healthy industrial workers chronically exposed to high ambient noise levels (> 85 dB [A]) without using ear protectors. The results indicated that under conditions of chronic noise exposure the cortisol level at the end of the workshift was high and almost reached the morning level. This elevation in cortisol excretion was accompanied by high levels of accumulated fatigue and postwork irritability. Attenuating the noise reaching the eardrum by 30 to 33 dB, by fitting the same workers with earmuffs for a period of 7 working days, resulted in a significant improvement in both psychological and physiological stress reactions. Besides decreasing noise intensity, no other changes were made, either to ongoing work activities or to the other characteristics of the ambient noise. The cortisol level declined steadily during the workshift and exhibited the normal cortisol diurnal rhythm. At the end of the workshift, this level was significantly lower (P < .05) than that observed under the chronic noise-exposure condition. There was also a concomitant reduction in reported fatigue (P < .05) and postwork irritability (P < .01). These findings demonstrate the "net" contribution of ambient noise to elevating stress reactions to regular work demands.