By a happy coincidence, the completion of this text coincided with the 200th anniversary of the discovery of gadolinite, the mineral with which the lanthanide story begins. For a group of elements which occur in only trace amounts biologically, and which have no known metabolic role, the lanthanides have spawned a surprisingly large biochemicalliterature. Se- rious interest in the biochemical properties ofthese elements can be traced to concerns about...