Data on selenium (Se) deficiency in Yugoslavia are summarized. These data include the selenium contents of stream sediments, rocks, soils, cereal crops grown in these soils, and human serum and scalp hair from several towns and regions. Analyses of human tissues in Yugoslavia show very low Se concentrations in both endemic and nonendemic areas. In some regions, including those with endemic villages, selenium contents of grains and human serum and hair are extremely low, approaching those in the low-selenium zone in China. According to the biological function of selenium, a very low intake of selenium may be a fundamental underlying condition that would predispose persons to attack by other agents in the development of Balkan endemic nephropathy.