Abstract: A method for the combined radioimmunoassay for the hormones triiodothyronine (T-3) and thyroxine (T-4) in serum or plasma, wherein the radiolabeled T-3 and T-4 reagents are T-3 and T-4 labeled with the same radioisotope. The hormones are extracted from the serum or plasma sample and separated from their binding proteins by adsorption to a crosslinked dextran gel at a highly alkaline pH. After washing away the dissociated proteins, a predetermined limiting amount of T-3 antibody is incubated with the gel and thereafter radiolabeled T-3 which has become extracted from the gel by antibody binding is washed away. Excess T-3 antibody and a predetermined limiting amount of T-4 antibody are then incubated with the gel and radiolabeled T-3 and T-4 which has become extracted from the gel by antibody binding are thereafter washed away.