The Cu-sarcosine-OH and Cd-MIDA-OH systems have been studied by differential pulse polarography (DPP) at a fixed total ligand to total metal concentration ratio and varied pH at 298 K and mu = 0.5 mol dm(-3) in the background of NaNO3. Both the metal-ligand systems show initially dynamic (labile), followed by semi-dynamic behaviour on the DPP time scale. It has been shown that the experimental and calculated DPP complex formation curves used previously only for labile metal-ligand systems can be employed for the modelling of all species formed in a solution and optimisation of their stability constants. The stability constants of ML and ML2 complexes as log beta were estimated for Cu-II and Cd-II as 7.75 +/- 0.02, 14.49 +/- 0.01 and 6.67 +/- 0.02, 12.00 +/- 0.02, respectively (all known hydroxide species of copper and cadmium, including polynuclear species, were incorporated into the metal-ligand-OH systems). The formation of the complex CuL2(OH) is suggested also and its stability constant as log beta has been estimated to be 16.2 +/- 0.2. Results reported here seem to be reasonable when compared with the literature data reported at 298 K and different ionic strengths.