This invention is directed to a ligand-receptor assay for determining the presence or amount of at least one target ligand, capable of competing with a ligand analogue conjugate for binding sites available on a ligand receptor, said ligand analogue conjugate comprising at least one ligand analogue coupled to a signal development element capable of emitting a detectable signal, in a fluid sample suspected of containing said target ligand, comprising the steps of:a. contacting said fluid sample with ligand analogue conjugate and ligand receptor to form a reaction mixture, the relative amounts of ligand analogue conjugate and ligand receptor being such that in the absence of target ligand, and subsequent to substantially equilibrium binding, substantially all of the ligand analogue conjugate is bound to ligand receptor;b. detecting the unbound ligand analogue conjugate;c. relating the detectable signal to the presence or amount of target ligand in the fluid sample. In one embodiment an optional means also is employed for removing receptor from the reaction mixture. In related claimed assay formats the analyte of interest may be either ligand receptor or ligand.