The term ultratrace element has been defined as an element with an established, estimated, or suspected requirement generally indicated by μg/day for humans. Between 1970 and 1984, it was suggested that 11 elements should be added to the list of ultratrace elements that included chromium, molybdenum, and selenium; these elements were arsenic, boron, bromine, cadmium, fluorine, lead, lithium, nickel, silicon, tin, and vanadium. Since 1984, it has been suggested that three more elements, aluminum, germanium, and rubidium, should be added to the list, and circumstantial evidence has continued to accumulate which indicates that several of the ultratrace elements in addition to iodine and selenium, particularly arsenic, boron, chromium, nickel, silicon, and vanadium, are more important in nutrition than currently acknowledged. This evidence includes findings from human studies suggesting that boron has an essential function or beneficial effect in calcium metabolism, brain function, energy metabolism, and perhaps immune processes; and that chromium has an essential function in potentiating insulin action in the metabolism of glucose and lipids, and/or a beneficial effect on diabetes resulting from inadequate synthesis of insulin or insulin resistance. The major shortcoming that has prevented the unequivocal acceptance of the nutritional importance of any of the ultratrace elements suggested as being essential since 1970 and chromium is that a specific biochemical function has not been identified for any of these elements. The current status of the evidence suggesting essentiality, the possible biological function, and speculated dietary need for each of the 15 elements without an identified biochemical function is reviewed. J. Trace Elem. Exp. Med. 11:251–274, 1998. Published 1998 Wiley-Liss, Inc.