Differential pulse polarography (DPP) and, especially, differential pulse anodic stripping voltammetry (DPASV) were applied to the study of the binding of Cd(II) by polystyrene latex particles. Some complications that arose in previous voltammetric studies of different heavy metal + polystyrene latex systems at low concentrations of the metal ion were considered. The problem consisted basically of noticeable differences between the stability constants computed from current data and those obtained from potential data. The results show that the metal-to-ligand ratio is a key parameter for understanding such problems, and that these could be related to the presence of a small minority of strong complexing sites. Complications derived from association-dissociation kinetics and/or from non-excess of ligand also might be involved. The various possibilities are discussed and some qualitative considerations and general guidelines are given, especially to define criteria to test the reliability of voltammetric measurements on heavy metal + colloid systems.