For the study of the relationship between styrene exposure and symptoms and signs of central nervous dysfunctions, 98 male workers occupationally exposed to styrene were given clinical, neurophysiological and psychological examinations; also a symptom survey was made. Urinary mandelic acid concentrations, measured once a week during five consecutive weeks, were used to express the exposure intensity. Different unexposed groups were used for reference. No exposure-response relationship was observed between symptoms of ill health and the urinary mandelic acid concentration, although the exposed group as a whole expressed significantly more symptoms than the reference group. The occurrence of abnormal electroencephalograms was about 10% in the group of workers with mandelic acid concentrations below 700 mg/l, but it was 30% among those whose mandelic acid concentration exceeded 700 mg/l, a level corresponding to the 8-h time-weighted average (TWA) of styrene exposure of about 30 ppm. With regard to psychological functions, the first change in visuomotor accuracy became discernible when the urinary mandelic acid concentration exceeded 800 mg/l. A more pronounced decrement appeared in both visuomotor accuracy and psychomotor performance when the mandelic acid concentration exceeded 1,200 mg/l, which corresponds to an 8-h TWA of styrene exposure of about 55 ppm.