The interaction of DNA with Fe³⁺, Al³⁺, Co(NH₃)₆³⁺ in a solution containing MnCl₂ was studied. It was shown that there exists a competition for the binding sites between Mn²⁺ and Al³⁺, while the binding of Mn²⁺ to DNA does not depend on the presence of Fe³⁺ and Co(NH₃)₆³⁺ in solution. We proposed that Fe³⁺ and Co(NH₃)₆³⁺ ions prefer to bind to phosphates, and Al³⁺ ions are capable to bind to the nitrogen bases of DNA.