Interaction between dioxovanadium(V) and ethylenediamine-N,N'-diacetic acid (EDDA) has been investigated by potentiometric and UV spectrophotometric measurements in an aqueous solution of pH = 1.00 to 2.50 at I = (0.1 to 0.9) mol.dm(-1) (NaClO(4)) and 25 degrees C. Different speciation models were used to detect the species, but the model that best fits the experimental data takes into account the formation of two species, VO(2)H(2)L(+) and VO(2)HL. Distribution diagrams for the main species at different ionic strengths have been calculated as a function of pH. The dependence on ionic strength of the stability and dissociation constants was studied by using the extended Debye-Huckel-type equation (EDH), specific ion interaction theory (SIT), and the parabolic model. All of these approaches gave comparable and satisfactory results. Literature data were also considered and compared.