Metal ion binding to biomaterials derived from cultured antheral cells of Datura innoxia has been investigated as a function of solution pH. Specifically, the binding of Ba2+, Cd2+, CU2+, Ni2+, and Sr2+ Was Studied at pH 1-6, inclusive, in 0.1 M MES solutions. For 10 mg . L(-1) metal ion solutions, maximum binding was observed for solutions at pH 5. The dependence of metal ion binding on solution pH was studied for the biomass both free in solution and immobilized in a polysilicate matrix. A significant change in the pH-dependent binding of each of these metals was observed when the cell material was immobilized. These variations in the impact of metal solution pH could not be explained by the Lewis acidity of the metal ions. The involvement of conformational changes of the macromolecular components of the material for the formation of metal-selective coordination sites is postulated.