The effects of environmental conditions on stress responses to mental work, were examined by measuring urinary catecholamine and cortisol excretion and salivary cortisol concentrations before, during and after an arithmetic calculation task under 90dB(A) white noise and quiet conditions. Adrenaline excretion increased similarly during the task under both environmental conditions. The salivary cortisol level was significantly higher than the pre-task level during the task with noise, but not under quiet, conditions. The subjects reported that they felt more irritable when performing the task with noise, than under quiet conditions. The results suggest that environmental conditions may affect on the pattern of hormonal response to mental work, which may be related to psychological states of the subjects.