Trace amount of molybdenum was measured by polarography in serum from 105 healthy adults and 159 patients with Keshan disease. Geometric mean molybdenum concentration in normal serum was found to be 6.2ng/ml (range: 1.5-25.0ng/ml), in serum of patients with latent and chronic type, the average level was 5.7ng/ml and 5.8ng/ml respectively (range: 1.7-33.7 ng/ml)There was no statistically significant difference between the molybdenum concentrations found in patients and healthy adults.In 80-85% samples the range of molybdenum concentration was found to be 3-11ng/ml.There was no significant difference between the molybdenum concentrations found in different age groups and sexes.