In the present work two main objectives were chosen. The first was the preparation for the execution of the magnetic phase separation technique, useful for the radioimmunoassay as well as for the most modern and most efficient immunoradiometric assay. The second objective, of a theoretical-practical kind and directly linked to the first, was the realization of a study about the precision of the technique with synthesized products compared with imported products and with two liquid phase separation techniques: the second antibody and polyethyleneglycol (PEG). This analysis was performed with the help of precision profiles built according to R.P.Ekins` recommendations. (author).