In a cross-sectional study the psychological test performances of a group of 36 male chlorine-alkali workers were compared with the level of exposure to mercury and to the corresponding results of referents. The mercury exposure had lasted for at least 10 years and had been controlled by regular health examinations and urine analyses. Several dose indicators were calculated. The more heavily exposed workers performed more poorly on the verbal intelligence test (Similarities) than the referents did. Impairments in the memory tests showed a statistically significant correlation with the actual exposure level, especially with the actual concentration of mercury in blood. The monitoring of mercury in blood can be useful in health surveillance programs. The level of mercury in the air was calculated from the dose indicators. The results support the recommended exposure limit of 25 micrograms/m3 for metallic mercury vapor in the air as a level avoiding adverse effects in exposed workers.