The interaction between anions of trihydroxy bile acids (BS-) (cholate, glycocholate, taurocholate, ursocholate, and hyocholate) and divalent transition metal ions (Cu2+, Cd2+, and Zn2+) was followed using polarographic reduction of the metal ion. For solutions containing 0.1 mM Me(2+) no interaction with BS- was observed at concentrations below 1 mM. At [BS-] between 1 and 10 mM slightly soluble complexes are formed, attributed to an interaction of Me(2+) with small aggregates of BS-. At concentrations above 10 mM BS- large ("micelle-like") aggregates are formed, bearing free COO- groups which increase their solubility. Exact concentration limits characterizing individual ranges depend on the nature of both BS- and Me(2+). Sequences of overall stability constants, solubilities, and ranges of formation of large aggregates indicate a similar stacking of hydroxy bile acid anions in both small and large aggregates. The stability of complexes with small aggregates increases in the sequence Cd2+ < Fe2+ < Pb2+ < Zn2+ < Cu2+, and their solubility in the sequence Fe2+ < Cu2+ < Cd2+ < Zn2+. The sequence of the concentrations at which large aggregates are formed in the presence of Me(2+) ions resembles the sequence of CMC values obtained in the presence of Na+ ions.