The effect of the reactant adsorption on square wave voltammetry of a 2-electron quasi-reversible redox reaction is analysed experimentally and theoretically. Current potential profiles and the characteristics of the peak curve and the peak potential were analysed at different pH and adsorption potentials for Cd-oxine complexes. The rate constants k(s) = 6, 1.3 and 0.4 s(-1) were obtained at pH 6.4, 7.8 and 11, respectively. Analytical applications were also considered.