Alterations in nutritional status may affect a number of biological functions via modifications in minerals and trace elements. Direct (assay of a mineral) and indirect (assay of a biological activity) tests for evaluating mineral status are reviewed herein, with emphasis on advantages and limitations. Special attention is given to serum zinc, erythrocyte membrane alkaline phosphatase, Cu, Zn superoxide dismutase selenium, and serum or intracellular glutathione peroxidase activity.