This monograph is intended as a reference for prospective or existing research groups engaged in the study of elements at the ultratrace level in clinical samples. In such an interdisciplinary cooperation, there is a need to bridge the gap between the analytical and the clinical scientist with information on the possibilities and the problems associated with the use of neutron activation analysis. This book is not a text book to convert a medical doctor into an analyst or the reverse, and many subjects are only briefly introduced before being discusses, but it is hoped that the exchange of ideas across the interdisciplinary boundary will be stimulated.