The stability constants of the 1:1 complexes formed between Mg2+, Cu2+, or Zn2+ (= M2+) and dGMP(2-), i.e., M(H;dGMP)(+) and M(dGMP), were determined by potentiometric pH titration in aqueous solution. It is shown that in all three M(dGMP) complexes the phosphate-coordinated M2+ interacts also to a certain degree with N7 of the nucleobase. The formation degree of the resulting macrochelates varies between 41 +/- 7% for Mg(dGMP) and 93 +/- 1% for Cu(dGMP). The connected increased complex stabilities for M(dGMP) are somewhat larger than those for M(GMP).