Simultaneous radioimmunoassay of thyroid hormones in unextracted serum

A combined radioimmunoassay for the two thyroid hormones is described which uses 125iodine labelled triiodothyronine and 131iodine labelled thyroxine. The assay employs a double antibody separation technique and is suitable for use with unextracted serum. The results from the simultaneous assay compare very well with the results obtained in the single assays, and the discriminating power and precision of the simultaneous assay is a least as good as in the single assays.