A longitudinal study was performed to investigate the behavioral changes associated with occupational exposure to organic solvents. An initial simple reaction time (SRT) test was performed on a group of steel workers who were exposed to vapor concentrations of solvents clearly exceeding threshold limit values (TLVs). A second SRT measurement was made six months following the completion of major improvements in the hygiene quality of the work environment which resulted in a reduction of exposure levels to 20% of the TLVs valid at the time. Approximately fifteen months after this measurement, a final SRT test was performed. The workers' performance on the SRT test improved over the three measurements. At the first measurement occasion SRT was found to be related to the degree of exposure, while no such relation could be observed on the following measurement occasions. The results indicate that the workers' central nervous functioning had been negatively affected by solvent exposure and that this effect was at least partially reversible in nature; they thus confirm the importance of changes which enhance the hygienic quality of the work environment.