Interaction of Watson-Crick adenine-thymine (AT) and guanine-cytosine (GC) base pairs with various metal (M) cations (Mg2+,..., Hg2+) were studied by nonempirical ab initio methods with inclusion of correlation energy. Cations were allowed to interact with the N7 nitrogen of adenine and the N7 and O6 atoms of guanine. All of the cations were described by Christiansen’s average relativistic effective potentials using the DZ+P basis set, while the 6-31G** basis set was used for the elements of base pairs. Disruption of the adenine-thymine as well as guanine-cytosine pairs in the presence of all studied cations is energetically more demanding than that for isolated base pairs; the addition stabilization of the base pair is about 100% for complexes with dication. The interaction is highly nonadditive. The three-body term is for the MGC complex considerably larger than that for MAT; the intercomplex charge transfer is also much larger for the former complex.