Abstract: A serum sample is heated at an alkaline pH to release folate and vitamin B.sub.12 from endogenous binders. A simultaneous radioassay for folate and vitamin B.sub.12 is effected by contacting the sample with binder for folate, binder for vitamin B.sub.12, folate labeled with one radioactive isotope and vitamin B.sub.12 labeled with another radioactive isotope, followed by separation of bound and free portions, and determination of the radioactivity of at least one of the portions. The amounts of folate and vitamin B.sub.12 present in the sample may be determined from standard curves.

Abstract: A serum sample is heated at an alkaline pH to release folate and vitamin B.sub.12 from endogenous binders. A simultaneous radioassay for folate and vitamin B.sub.12 is effected by contacting the sample with binder for folate, binder for vitamin B.sub.12, folate labeled with one radioactive isotope and vitamin B.sub.12 labeled with another radioactive isotope, followed by separation of bound and free portions, and determination of the radioactivity of at least one of the portions. The amounts of folate and vitamin B.sub.12 present in the sample may be determined from standard curves.

Abstract: A serum sample is heated at an alkaline pH to release folate and vitamin B.sub.12 from endogenous binders. A simultaneous radioassay for folate and vitamin B.sub.12 is effected by contacting the sample with binder for folate, binder for vitamin B.sub.12, folote labeled with one radioactive isotope and vitamin B.sub.12 labeled with another radioactive isotope, followed by separation of bound and free portions, and determination of the radioactivity of at least one of the portions. The amounts of folate and vitamin B.sub.12 present in the sample may be determined from standard curves.

Abstract: In an assay wherein radiolabeled substance bound to a receptor is separated from unbound radiolabeled substance, such separation is effected by the use of a combination of a particulate adsorbent and a thickening agent to decrease adsorption time. The procedure can be employed, for example, in separating bound iron from free iron in a total or unsaturated iron binding capacity assay.

Abstract: Solid substrate is coated with a receptor, with a limited portion of the receptor being reversibly coated with a labeled form of a ligand to be assayed, whereby during an assay procedure the labeled form of the ligand is free to re-equilibrate with the receptor in competition with the ligand to be assayed.

Abstract: A receptor is coated on a plastic substrate, such as a tube, from a solution containing a blocking agent for the receptor sites to prevent adherence of the receptor sites to the plastic substrate, and a deaggregating agent for the receptor to prevent adherence in dimers or aggregates which block receptor sites, thereby reducing receptor requirements.

Abstract: In the radioassay of folates, the standard is prepared by using folic acid (pteroyl glutamic acid; PGA) as the standard folate at a pH of 9.2 to 9.4. At such pH values, folic acid and 5-methyltetrahydrofolic acid (the predominant folate in human serum) have essentially identical reactivity towards folate binders, whereby folic acid can replace unstable 5-methyltetrahydrofolic acid standard for such assays.

Abstract: Tritiated succinylated derivatives of cyclic nucleotides, in particular multitritiated succinylated cyclic adenosine monophosphate, useful in the radioimmunoassay of cyclic nucleotides, and maleyl derivatives of cyclic nucleotides useful in the production of the tritiated derivatives.