Abstract: A method and reagent composition provide for the removal or blocking of serum interferences in liposome immunoassays. A carrier or liposome exhibiting at least one domain of phosphoryl ester groupings different from those of the marker liposome is introduced into the reaction mixture, whereby endogenous interfering species competitively bind to such carrier or liposome rather than to the marker liposome. Also, soluble phosphoryl ester groupings can be introduced into the reaction mixture which react with such endogenous species and further reduce serum interferences.