Sir.—We have read with interest the review articles on trace elements in the young infant by Dr Shaw (Journal 133:1260-1268, 1979; 134:74-81, 1980). It is evident that knowledge of trace-element metabolism is of growing importance in the study of many diseases. Although Dr Shaw gives an excellent treatment of some of the well-known trace elements, we would like to comment on his decision to omit a discussion of molybdenum "because so little is known about its role in the metabolism of the fetus and young infant."
A considerable amount of knowledge about molybdenum metabolism in humans has been gained over the past few years. For example, an inverse relationship between copper and molybdenum levels in fetal liver has been established.1 In addition, it is now known that molybdenum is an essential component of the human. enzymes sulfite oxidase, xanthine dehydrogenase, and aldehyde oxidase.2 The metal in these