In a study of the effects of low lead exposure on psychological performance, 49 exposed workers and 24 controls were given a psychological test battery. All the lead workers had been under regular monitoring during their entire exposure time, and only workers whose maximal blood lead concentration had never exceeded 70 μg/100 ml were included in the study. At the time of the examination, the mean blood lead level of the exposed group was 32 ± 11 μg/100 ml. Comparisons were made both between exposed and non exposed workers and within the exposed group. In the latter case, the maximal, the average and the actual blood lead concentrations were used as measures of uptake. The most important finding was a significant relationship between impaired psychological performance and lead uptake within the exposed group. The performances that were most affected by lead depended on visual intelligence and visual-motor functions. Age and neuroticism did not explain these relationships. The impairment of psychological performance correlated better with the average than with the maximal or actual blood lead concentration. Considering that no single blood lead concentration had ever exceeded 70 μ/100 ml, these findings indicate that the threshold for impaired performance lies below that level.