Abstract: The chloramine T procedure is employed to provide radioiodinated T.sub.3 and radioiodinated T.sub.4 from T.sub.3 and T.sub.4, respectively, at specified pHs and mole ratios to provide for long shelf life. T.sub.3 is also radioiodinated to high specific activity radioiodinated T.sub.4, and purified after a specified waiting period to remove radioactive non-antigenic contaminants and thereby provide a long shelf life.

Abstract: An analyte, such as an antigen, is initially contacted with a receptor (antibody) bound to a solid support, in the absence of tracer, followed by removal of unbound analyte and contacting with tracer. By separately contacting the receptor with analyte and tracer, sensitivity is increased.

Abstract: Automated assay for qualitative determination of thyroid hormone binding capacity of a serum sample in which serum and T.sub.3 tracer are caused to flow through a chamber containing a T.sub.3 binder supported on a solid support. The amount of T.sub.3 tracer which passes through the chamber, and the amount of T.sub.3 tracer bound to the binder in the chamber are determined to thereby determine the percent of bound T.sub.3 tracer. Such percent is then compared with the percent of T.sub.3 tracer bound in a referenced sample to qualitatively determine the T.sub.3 binding capacity of the serum sample.

Abstract: In an automated assay employing a reusable immobilized binder in a flow-through chamber, the binder is supported on a cotton support preferably mercerized absorbent cotton. Such cotton support prevents plugging when using free serum or plasma samples, and in addition, does not compress, has good flow properties, is easily handled, has low non-specific binding of proteins and steroids and is stable.

Abstract: The chloramine T procedure is employed to provide radioiodinated T.sub.3 and radioiodinated T.sub.4 from T.sub.3 and T.sub.4, respectively, at specified pHs and mole ratios to provide for long shelf life. T.sub.3 is also radioiodinated to high specific activity radioiodinated T.sub.4, and purified after a specified waiting period to remove radioactive non-antigenic contaminants and thereby provide a long shelf life.

Abstract: Automated radioimmunoassay directly from serum, for those antigens present in serum in relatively small amounts, is accomplished by use of an immobilized immunoadsorbent having an excess of antibodies, specific to the antigen, covalently bonded to a particulate substrate. The serum is diluted and preincubated in the presence of a radioactive labelled antigen and an antibody specific to the antigen. The preincubated mixture is flowed through the immobilized immunoadsorbent and the labelled and unlabelled antigen not bound to the antibody in preincubation are bound to the immobilized immunoadsorbent while the labelled and unlabelled antigen bound to the antibody during preincubation flow through the immunoadsorbent. An eluting solution is flowed through the immunoadsorbent to release the antigens bound thereto for reuse of the immunoadsorbent.