An assay based on the competition between a labelled and an unlabelled ligand in the reaction with a receptor binding agent (e.g. antibody, receptor, transport protein).
Source:
PAC, 1994, 66, 2513. 'Nomenclature for radioanalytical chemistry (IUPAC Recommendations 1994)' on page 2516 (https://doi.org/10.1351/pac199466122513)