The relation of exposure to styrene to measures of nervous system function was investigated in 70 men working in four factories in the Montreal area of Quebec. Mild sensory nerve conduction deficits were found, the proportion with such deficits rising from 23% in those exposed to less than 50 ppm to 71% in those exposed to more than 100 ppm. Reaction time was slower for those with a larger body burden, as indicated by area under the excretion curve, and for those who failed to clear the metabolite during the weekend. No slowing in conduction time was found among a small group of five men exposed to more than 100 ppm for less than four weeks. There was some evidence that both central and peripheral slowing recovered when workers were removed from exposure. Uptake, storage, or elimination of styrene was influenced by the physical demands of the work, skinfold thickness, cumulative exposure, and alcohol consumption. Nevertheless, only the wearing of a mask and current consumption of alcohol were associated with a lower risk of sensory conduction deficit. While there was no clear indication that neurotoxic effects were related to individual differences in the capacity to metabolise high concentrations of styrene, measurement of urinary metabolites may be helpful in identifying those at highest risk.