It had been shown that subclinical impairment of the peripheral nerves may occur in neurologically symptom-free lead workers. In a cross-sectional study, 78 workers from two storage battery plants and one engineering shop were studied; their lead exposure had been monitored with regular blood lead measurements (PbB). The reference group comprised 34 unexposed manual workers. An exposure-effect relationship between occupational lead exposure and nerve functions emerged, as nerve conduction velocities decreased with increasing PbBs. The strongest correlations were found between PbB measures and sensory and motor conduction velocities of the median nerve. An exposure-response relationship also emerged as the proportion of subjects with abnormal nerves increased with increasing exposure levels. In a prospective study 24 workers were followed-up from the commencement of their lead work for one year and 16 for two years. The lead exposed showed a tendency of decreasing conduction velocities of arm nerves, but as a group they did not differ statistically significantly from the control group. When the lead exposed were divided into two groups using the median PbBs as the splitting point, the ones with PbBs over 30 micrograms/100 ml showed slowing of serveral nerve conduction velocities, while in the lower exposure the conduction velocities remained at the initial level. Again the clearest difference was noted in conduction velocities of the median nerve. Nerve conduction velocities, especially in the arm nerves slow down in lead exposure and this impairment is caused by really low lead exposure as noted in the prospective follow-up study, which can be regarded as intervention study.