An initial goal of this research project was to develop, evaluate, and compare different assays for use in the quantification of salmon calcitonin ( (\mathrm{sCT}) ) adsorption onto various pharmaceutical surfaces. The three assays examined varied in the use of ({ }^{125} \mathrm{I}) radiolabeled sCT in an attempt to demonstrate analogous findings between the use of labeled and unlabeled material. The first assay involved a competitive adsorption reaction of ({ }^{125}) I-sCT with cold sCT. The second technique employed a colorimetric protein assay and the third was a HPLC procedure utilizing UV absorption. The latter two techniques were used to quantitate the sCT concentration and determine loss of sCT from solution without the use of radiolabeled material. During the development of the ({ }^{125} \mathrm{I}-\mathrm{sCT}) adsorption assay it became apparent that the four ({ }^{125}) I-sCT species were produced during the iodination process. Each of these species exhibited different interfacial characteristics. A purified fraction of ({ }^{125} \mathrm{I}-\mathrm{sCT}) which was shown to be unmodified monoiodinated sCT behaved interfacially like unlabeled SCT. Each assay possessed unique advantages and disadvantages in development and application. The ({ }^{125} \mathrm{I})-sCT and colorimetric assays were the easiest and fastest to perform. The HPLC was the more accurate of the two cold techniques. After developmental refinements, all three assays showed comparable results both qualitatively and quantitatively. The results from the assays showed that adsorption of SCT to polypropylene was negligible. Salmon calcitonin adsorbed to borosilicate Type I glass at an amount of 200 to (250 \mathrm{ng} / \mathrm{cm}^{2}), within the concentration range of 2.5 to (20 \mu \mathrm{g} / \mathrm{ml}). 1994 Academic Press, Inc.