The DRG T3 Total ELISA is an enzyme immunoassay for the quantitative in vitro diagnostic measurement of total T3 (triiodothyronine) in serum and plasma Measurement of serum triiodothyronine concentration is generally regarded as a valuable tool in the diagnosis of thyroid dysfunction. This importance has provided the impetus for the significant improvement in assay methodology that has occurred in the last two decades. The advent of monospecific antiserum and the discovery of blocking agents to the T3 binding serum proteins has enabled the development of procedurally simple radioimmunoassays (1,2). The DRG T3 Total ELISA Kit is a solid phase enzyme-linked immunosorbent assay (ELISA), based on the principle of competitive binding. The microtiter wells are coated with a polyclonal goat-anti-mouse antibody. Standards, controls and patient serum incubate together with Assay Reagent containing monoclonal anti-T3 antibodies. In the following incubation with Conjugate the endogenous T3 of a patient sample competes with the T3-horseradish peroxidase conjugate for a limited number of insolubilized binding sites. After incubation the unbound conjugate is washed off. The amount of bound peroxidase conjugate is inversely proportional to the concentration of T3 in the sample. After addition of the substrate solution, the intensity of colour developed is inversely proportional to the concentration of T3 in the patient sample.