OBJECTIVE To investigate the systemic changes of iron metabolism following manganese exposure. METHODS Ninety-seven welders and 91 workers with no history of exposure to manganese were recruited from the same factory in Beijing serving as the exposure group and the control group respectively. The welding rods used were type J422. The concentration of the manganese in the air of the work place was determined respectively with the national standard method. The serum iron and manganese, ferritin, transferrin and transferrin receptors were measured with the graphite furnace atomic absorption spectrophotometry and ELISA in both groups. RESULTS The permissible concentration-STEL of ambient Mn in welders' breathing zone ranged from 0.53 mg/m(3) to 2.19 mg/m(3), while the permissible concentration-TWA of ambient Mn was between 0.29 mg/m(3) and 0.92 mg/m(3) in the breathing zone of the workplace. Serum Mn and Fe concentrations in welders were about 1.40 times (P < 0.0l) and 1.2 times (P < 0.01), respectively, higher than those of control subjects. At the same time, the transferrin concentrations in serum were significantly higher (about 1.2 times, P < 0.05) in welders than in controls. In contrast, transferrin receptors were significantly lower (about 1.2 times) in exposed subjects than controls (P = 0.001). There was no difference in serum ferritin between the two groups (P = 0.112). Although there was no significant trend, the serum ferritin level was increased by 18% in comparison with that of the control. The abnormal percentage of serum Fe and Serum Mn in welders were 55.67% and 67.01% respectively, higher than those of control subjects. In addition, the correlations between all indicators and the duration of employment were not observed. CONCLUSIONS The long term exposure to the manganese can induce the disorder of the iron metabolism, which is found in the expression of increase of the serum iron and transferrin as well as the decrease of transferrin receptors.