Abstract: The present invention provides a method of performing an immunoassay of a ligand in a liquid sample wherein two independently measureable enzyme labels are separately conjugated to two or more components or populations of components of the assay system and, after completion of the complexing reaction, substantially all of the first enzyme label and a proportion of the second enzyme label are removed from the assay mixture, the proportion of the second label removed being related to the amount of the said ligand and the assay determined from a measurement of said proportion of the second label being normalised by comparison with a measurement of the total first label removed.In this way, manual pipetting errors and other assay procedural errors can be corrected for.