The effect of several surfactants on the formation of the fluorescent ternary complex oxalate-Alizarin Red S-zirconium(IV) has been studied. In weakly acidic medium and in the presence of cationic surfactants, such as cetylpyridinium chloride, total complex formation is achieved, whereas in aqueous medium or in the presence of non-cationic micelles no significant changes are obtained in comparison with the formation of the non-fluorescent binary complex Alizarin Red S-zirconium(IV). The fluorescence characteristics of this system allowed the establishment of a simple and very sensitive method for the spectrofluorimetric determination of oxalate. The ternary complex formed exhibits its highest fluorescence signal at 605 nm with excitation at 490 nm. In these conditions, the method presents a IUPAC detection limit of 4.4 ng ml(-1). The procedure has been satisfactorily applied to a biological fluid and a vegetal tissue.