Abstract: A hypothyroid control serum for use in assay of thyroid function of serum with a reagent antiserum, said control comprising (a) serum from which triodothyronine and thyroxine have been stripped and (b) low-affinity antibody against triiodothyronine.

Abstract: Free analytes in samples containing free analytes and receptorbound analytes are determined by absorbing at least a portion of free analyte from the sample with insolubilized receptor or receptor which is then made insoluble, washing the insoluble receptor, adding labelled sample analyte or labelled sample analyte receptor, incubating, washing the insoluble phase free of the soluble phase and determining the label in either phase. The method solves a long standing need in the assay of free thyroid hormones.

Abstract: Compounds useful as tracers in the radioimmunoassay of barbiturates: ##STR1## wherein (a) R.sub.1, R.sub.2 and R.sub.4 are identical to the substituents found at these positions in the barbiturate which is to be assayed;(b) at least one R.sub.3 is a radioiodinatable radical; and(c) if only one R.sub.3 is a radioiodinatable radical then the remaining R.sub.3 is identical to the substituent found at this position in the barbiturate which is to be assayed; and the radioiodinated derivatives of said compounds.

Abstract: Derivatives of 5,5-diphenylhydantoin having the following structural formula: ##STR1## where R is 2-acetyl, 3-propionyl, 4-butyryl or 5-valeryl and X is an unlabeled or radioiodinated amino radical; e.g., (tyrosine, histidine, tyrosinol, histamine). A preferred compound is radioiodinated 5,5-diphenyl-3-(5-valeryl-N-tyrosine) hydantoin. The iodine isotope may be iodine -125 or iodine-131.

Abstract: Derivatives of 5,5-diphenylhydantoin having the following structural formula: ##STR1## where R is 2-acetyl, 3-propionyl, 4-butyryl or 5-valeryl and X is an unlabeled or radioiodinated amino radical; e.g., (tyrosine, histidine, tyrosinol, histamine). A preferred compound is radioiodinated 5,5-diphenyl-3-(5-valeryl-N-tyrosine) hydantoin. The iodine isotope may be iodine-125 or iodine-131.

Abstract: Gamma globulins from antisera having a titer so low in selected antibodies that the antibodies adsorbed on a surface of polymeric material are ineffective for use in immunoassay, are cross-linked, then adsorbed on the polymeric surface to provide an immunologically active coating. Binding proteins incapable of effective adsorption on polymeric surfaces are cross-linked with gamma globulin, then adsorbed on a surface of polymeric material capable of adsorbing gamma globulin to provide a specific binding protein coating. Kits containing test tubes having such coatings are used in radioimmunoassay, in enzyme immunoassay, and in fluoroimmunoassay.