Methods and test devices for detecting the presence or amount of target ligand in non-competitive sandwich ligand-receptor assay processes. Antibodies which bind to the complex of ligand receptor and target ligand but do not bind significantly to the ligand receptor and which bind the target ligand with substantially less affinity than the complex are taught and their uses described. These assays can be used to eliminate the "hook" effect in non-competitive sandwich assays. Furthermore, the antibodies are selected and assay methods described so that, as a result of the assay process, no detectable response is observed due to the binding of antibody and ligand receptor in the absence of target ligand.