The authors report the development of a novel thin film multilayer immunoassay technology. The technology is applied to therapeutic drug monitoring and thyroid hormone testing in serum or plasma and can be extended to assays of other low molecular weight analytes. The assay detection range spans five orders of magnitude, from 1 x 10(-3) to 1 x 10(-8) M. The assay element comprises of multilayer coated chip, containing the active reagents in an agarose matrix and a plastic module serving both as a holder and a spreader. The assays are in the fluorescent competitive immunoassay format of the ligand displacement mode and are performed on an automated instrument with random access capability. The assays are fast and reliable and gave very good agreement when compared to reference methods.