Among other elements (manganese, molybdenum, cadmium, mercury, lead, nickel), the levels of selenium in healthy human sera (n = 56) and plasma (n = 15) were measured by ICP spectrometry. It was ascertained by the multielement analysis that of 40 nineteen year-old males (from 28 different villages in one county 15 showed lower than detectable levels of selenium in their sera (n = 25) and plasma (n = 15) samples. For this reason, the selenium contents of the sera of 31 blood donors were determined by the ICP spectrometry, with hybrid generation. By this same technique the selenium in sera of 16 men aged between 24-60 years (mean = 43.3 years) was measured as 24.06 micrograms/l (13-42 micrograms/l), while in 15 women between the ages of 19-64 years (mean 39.3 years) it amounted to 20.86 micrograms/l (11-31 micrograms/l). In 28 cases from 40 samples (25 sera and 15 plasma) the concentration of molybdenum was smaller than the detectable limit (less than 0.0011 mg/l). Firstly, these results prove that amongst healthy individuals, in Hungary, molybdenum and selenium deficiency states exist. The authors conclude that there is a relationship between these deficiency states, as risk factors, and the frequently occurring diseases (malignant tumours, cardiovascular diseases, etc.) in Hungary.