Abstract: A hapten-linker-large group conjugate for use in a rapid assay, wherein the assay is kinetic-based not approaching equilibrium, the hapten-linker-large group conjugate being of the general formula: X—W—Y-Z wherein: X is a hapten; W is an optional thioether or ether group;Y is a linker of 10 or more atoms in length; and Z is a large group of sufficient size to provide steric hindrance with respect to the binding of X to a ligand in the absence of Y. Also provided are processes for the production of the conjugates, assay methods and kits. The assays of the invention utilising conjugates of the invention [(5)-OVA] provide a better sensitivity than the same assays with conjugates with shorter linkers [(2)-OVA and 3-OVA].