To clarify the effects of organic solvents on auditory function, the upper limit of hearing was measured with 93 male workers exposed to organic solvents in six factories producing buttons and one factory producing fiber-reinforced plastic baths. Special medical examinations and environmental monitoring of the organic solvents were also done. The upper limit of hearing was significantly lower than the standard upper limit age curves for males, although the levels of environmental monitoring were lower than the permissible concentration of the organic solvents. It deteriorated in workers exposed to the organic solvents for more than 5 yr. Its deterioration was related to the levels of environmental monitoring of styrene and the mandelic acid concentration in urine. It deteriorated dose dependently as the levels of environmental monitoring of styrene increased. The chronic exposure to styrene may cause the deterioration of the upper limit of hearing. Those whose special medical examinations for organic solvents were normal, showed the deteriorated upper limit of hearing. It is suggested that the upper limit of hearing is a sensitive method for the biological response monitoring of styrene on workers.