Complex formation between 2-hydroxybenzohydroxamic acid (salicylhydroxamic acid, H(2)Sax) and metal ions Me2+ (with Me2+ = Cu, Ni, and UO22+) was investigated using a potentiometric methodology at 25 degrees C, and in 1 M NaClO4. The measurements have been performed using a glass electrode for Ni2+ and UO22+ and in the case of Cu2+ also an amalgam electrode. The molar concentrations of the metals ranged from 5.0.10(-4) mol.dm(-3) to 1.0.10(-2) mol.dm(-3), whereas the concentration of salicylhydroxamic acid was chosen in the interval 1.10(-4) mol.dm(-3) to 0.02 mol.dm(-3). The potentiometric data are consistent with the presence of species CuH-1(H(2)Sax)(+), CuH-2(H(2)Sax), NiH-1(H(2)Sax)(+), NiH-2(H(2)Sax), NiH-3(H(2)Sax)(2)(-), UO2H-2(H(2)Sax), UO2H-3(H(2)Sax)(-), and UO2H-4(H(2)Sax)(-2). Medium effects on the constants were calculated using the specific interaction theory (SIT).