Abstract: A method for quantitatively and/or qualitatively assaying an analyte in a sample, wherein the analyte is a receptor binding compound, has low detection limits equivalent to those of radioreceptor assays. The method comprises the steps of a) contacting the sample with material comprising a receptor for the analyte in order for receptor-analyte binding to occur and b) further contacting the sample with a detectable ligand for the receptor in order for receptor-ligand binding to occur, followed by c) separating the resulting receptor bound and free fractions, d) subjecting the receptor bound fraction to dissociating conditions releasing the ligand from the receptor and e) assaying for the dissociated ligand in a manner known per se for the detection of the detectable ligand.