Abstract: An improved specific binding assay method and reagent for determining a ligand in a liquid medium employing, as an enzyme-cleavable substrate label, a residue having the formula:G-D-Rwherein G is a glycone, D is a dye indicator moiety, and R is a linking group through which the label residue is covalently bound to a binding component of a conventional binding assay system, such as the ligand, an analog thereof, or a specific binding partner thereof. The monitored characteristic of the label is the release of a detectable product, usually a fluorogen or chromogen, upon enzymatic cleavage of the glycosidic linkage between the glycone and the dye indicator moiety. The assay method may follow a homogeneous or heterogeneous format. The preferred glycone is a .beta.-galactosyl group and the preferred dye indicator moiety is an umbelliferone residue.