The binary and ternary systems of Cu(II), Co(II), Ni(II), Zn(II), Cd(II), Mn(II), Mg(II), and Ca(II) metal ions with the hydroxamic acids, acetohydroxamic acid (Aha), benzohydroxamic acid (Bha), and salicylhydroxamic acid (Sham), and diamines, ethylenediamine (en), 1,3-diaminopropane (da r), and o-phenylenediamine (o-pda), were investigated potentiometrically at 25 degrees C and I = 0.10 mol center dot dm(-3) (NaNO(3)) in aqueous solution. The acid-base properties of the ligands were investigated. The potentiometric titration curves show that the ternary complexes are formed in a stepwise manner. The stability constants of the binary and ternary complexes were calculated on the basis of computer analysis of titration data. The order of stability of the binary and ternary complexes in terms of the nature of hydroxamic acids, diamines, and metal ions was investigated and discussed. The relative stability of ternary complex species is expressed in terms of Delta log K and % R.S. parameters. The distribution of binary and ternary complexes in solution was evaluated. Evaluation of the effect of temperature of the medium on both the ionization process of the ligands and complex formation for the M(II)-en-Sham (M(II) = Cu(II), Co(II), and Ni(II)) ternary systems has been studied along with the corresponding thermodynamic parameters. The complexation behavior of ternary complexes is ascertained using conductivity measurements. In addition, confirmation of the formation of ternary complexes in solution has been performed using cyclic voltammetry measurements.