Recommendations for daily dietary intakes of copper and zinc have been made by the National Academy of Sciences during the last decade. As a result there is increasing interest in analytic techniques for accurate and precise assessment of these trace elements in human tissues, including blood. In addition, the importance of standardizing techniques for the collection, preparation, and analysis of biologic samples is now recognized. The necessity for preventing contamination or losses requires careful monitoring at each step, from collection to analysis. Likewise, precision and accuracy must be established for techniques and certified reference standards employed. The selection of an ideal anticoagulant for preparing plasma for copper and zinc analyses is receiving increased attention. The discrepancy observed regarding higher concentrations (10-15%) of zinc and copper in serum than citrated plasma remains to be resolved. Following analysis and summary of the data, interpretation of the results is of paramount importance. It must be remembered that abnormal plasma or serum zinc or copper concentrations do not necessarily reflect true aberrations in metabolism, since several conditions (disease and nondisease) can also influence these indices of trace element nutriture. Immediate attention must be given to advancing the concept that trace element analysis of biological materials requires special collection, storage, and analysis precautions.