Selenium, the element of the moon, in life on earth

The present status of selenium biochemistry is reviewed with particular emp hasis on biomedical problems related to the selenium status of humans and e xperimental animals. Historical milestones of selenium biochemistry startin g from the identification of the first selenoenzymes up to the elucidation of prokaryotic and eukaryotic selenoprotein boisynthesis are compiled. Topi cal hypotheses on the biological role of selenium in general and of individ ual selenoproteins in respect to antioxidant defense, redox regulation of m etabolic processes, thyroid function, spermatogenesis, oncogenesis, and ath erogenesis are critically evaluated.