BACKGROUND:Whether long time exposure to the lead concentration which is withinthe state allowed range will cause any bad effects on people's health?OBJECTIVE: To investigate the nerve conducting velocity (NCV) and other biological indices of workers who are exposed to low concentration lead.DESIGN: It was an investigation and the subjects were workers exposed to low concentration lead.SETTING: Occupational Disease Department and Electrophysiological Department of Xinhua Affiliated Hospital of the Shanghai Second Medical University.PARTICIPANTS: In lead contact group were 66 heat treatment workers who were exposed to lead and received physical examination from September 2000 to October 2002. In control group were 40 office workers that worked at the same factory but were not exposed to lead.METHODS: Questionnaire and laboratory examination were adopted for measurement of NCV and other biological indices like blood lead, blood zinc protoaetioporphyrin (ZPP), blood free protoporphyrin (FPP) and hemoglobin content in the two groups. And the relative risk analysis was conducted.biological indices in both groups.RESULTS: All the 106 subjects entered analysis stage. In lead contact group there were 34 workers of more than 10 working years and the other ulnar nerve in those of over 10 working years were faster than those in control group [(50.11 ±4.76) m/s, (63.11±2.58) m/s vs (47.59±4.86)m/s,those of over 10 working years was higher than those of less than 10years [(0.568±0.28), (0.425±0.31) μmol/ L, P ＜ 0.05]. So was the FPP level [(2.24±0.32), (2.09±0.27) μmol/L, P ＜ 0.05] and urine lead level [(0.087±0.008), (0.083±0.007) μmg/L, P ＜ 0.05]. The ZPP level of those of over 10 working years was also higher than those less than 10 years [(1.42±0.33) μmol/L vs (1.25±0.35) μmol/L, P ＜ 0.05] and control [(1.42±0.33) μmol/L vs (1.22±0.44) μmol/L, P＜ 0.05]. The hemoglobin of those of over 10 working years was lower than those of less than 10 years [(12.26±4.5) g/L vs (14.55±4.81) μmol/L, P ＜ 0.05] and control [(12.26±4.5) g/L years presented abnormality in conducting sensory signals and the abnormality rate was 3% (1/32). Whereas four cases in those with more than 10working years did so and the abnormality rate was 12% (4/34). As for biological indices, one case in those less than 10 working years was beyond normal values (abnormality rate 3%) and five did so in those of over 10working years (abnormality rate 15%). It could be seen that changes in both NCV and biological indices of those of over 10 working years were more serious than those les than 10 years exposure with the relative risks of 4.1 and 5.3 respectively.CONCLUSION: Persistent exposure to lead not only alters biological indices but also damages nervous system in different degrees. Sensory verve of lower extremities and motor nerves of upper extremities are usually damaged first. Peripheral nerve injury is common in workers of over 10 working years. Because the regeneration of nervous system is poor, so the nerve injury is usually irreversible. Therefore the neuroelectrophysiological changes always predict early nerve injury and so neuroelectrophysiological monitoring can be adopted for prevention of nerve injury.