Abstract: Methods are provided for reducing non-specific interference in competitive protein binding assays employing as the labeled reagent a fluorescent conjugate of a hydrophobic ligand conjugated to a fluorescer, which in turn is bound to a water soluble polysaccharide carrier ("fluorescer conjugate reagent"). In order to reduce non-specific interference from physiologic samples, the fluorescent reagent is combined with a lipid substituted neutral support, under conditions which provides two binding fractions: a first weakly binding fraction which is relatively free of non-specific interference in a competitive protein binding assay employing physiological fluids; and a second fraction, which more strongly binds to the lipid substituted support.