Thematic series: metals in biology.

Metals are important in biochemistry, and the concentrations of many are highly regulated. This prologue introduces the thematic series "Metals in Biology," which includes minireviews on three metals: iron, copper, and selenium. Deficiencies and excesses of all three of these metals cause problems in human health. The three minireviews deal with regulation of iron homeostasis, the roles of copper metabolism in cell regulation and disease, and the functions of selenoproteins.