[en] The paper deals with the investigation of U(VI) and Fe(III) state in the wide range of pH and metal-ion concentrations. A set of methods (ultrafiltration, adsorption on glass surface, migration in electric field, ion exchange, dialysis, spectrophotometry) were used to determine the region of mono- and polynuclear hydroxide complex formation. Differe Differences in sorption abilities for hydroxo complexes of various metal ions can be used presumably in the development of fractionation and separation methods for these elements from solutions. (T.G.)