In Donnan dialysis aqueous samples are separated from receiver electrolytes by an ion exchange membrane. The present work demonstrates that the dialysis of metals into salt solutions occurs in proportion to the sum of the concentrations of the free metal and the metal held in the form of labile complexes; however, with strongly acidic or chelating receivers, the dialysis occurs in proportion to the total soluble metal. Hence, Donnan dialysis provides the basis for a rapid estimation of the total soluble (i.e., free plus labile complexed) metal and nonlabile-complexed metal. The method is demonstrated with Pb, Zn, Cu, and Cd complexes of glycine, humic acid, and nitrilotriacetic acid and is applied to a lake water sample. The results are compared to values obtained from an established approach that utilizes stripping voltammetry and separations with a chelating ion exchange resin.