The accuracy and reproducibility of an automated method has been assessed and the normal range for total serum organic iodine found to be 3.9-7.5 µg./10O ml., mean 5.7 µg./100 ml. Preliminary resin treatment of serum has been shown to be effective in removing normal concentrations of inorganic iodine. In the case of serums having grossly elevated inorganic iodine levels of up to 100 µ g./10O ml., the resin extracts more than 96% of the halide, but the unabsorbed iodine may invalidate the estimation. The resin can extract organic iodine from serum but the process occurs very slowly and it is of practical importance only if serums are allowed to stand over resin for longer than 24 hr.