A new experimental procedure for chicken plasma ferritin based on the method of Luxton et al. has been carried out. All biologic reagents used were obtained in our laboratory: Ferritin from chicken liver, antiferritin antiserum from rabbits and anti-rabbit IgG from goat. Chloramine T procedure was applied to label ferritin with 125I. The iodinated protein was removed from free iodide by use of three chromatographic columns of Sephadex G-25, Sephadex G-200 and Sepharose 6B. Separation of the first antigen-antibody complex was carried out by the double antibody method. The assay working range covers from 21.8 up to 175 ng/ml. As ferritin concentration is higher in chicken plasma than in human, various plasma dilutions ranging from 1/16 to 1/64 were used.