Fifty-four subjects chronically exposed to high manganese concentrations due to professional melting of iron-manganese alloys have been examined. The threshold limit value was exceeded 3 to 4-fold. The minimum length of employment in exposure was 5 years, whereas the average-17.7 years. Control groups were matched by age, length of employment and energy expense. Among the determined parameters, i.e. IgG, IgA, IgM concentrations in blood serum and C3 and C4 elements of the complement--only the IgM concentration was significantly lower, whereas the others were not significantly different from those in relevant control groups.