Serum iron may be directly measured without protein precipitation, by incubation in an acetate buffer in the presence of a reducing agent and sulfonated bathophenanthro line. Mercaptoacetic and ascorbic acids have proved to be suitable reductants. Values obtained for serum iron by this procedure show excellent correlation with a trichloro acetic acid precipitation technic. Bilirubin interference may be compensated for. Hemoglobin interference is significant at values above 30 mg./100 ml. Lipid interference is not significant at concentrations below 1,960 mg./100 ml. The iron chelators, ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), and desferrioxamine do not interfere. Both unsaturated iron-binding capacity (UIBC) and total iron-binding capacity (TIBC) may be estimated; values for both show good correlation. Serum iron, TIBC, UIBC, and % saturation values obtained from a group of children aged 4-12 years are presented. The advantages of the direct technic for serum iron, TIBC, and UIBC are simplicity and sensitivity.