The synthesis, spectroscopic, and electrochemical properties of trans-[L(Pyr)(NH3)4RuII/III] (Pyr = py, 3-phpy, 4-phpy, 3-pnpy, or 4-bnpy; L = H2O, Guo, dGuo, 1MeGuo, Gua, Ino, or G7-DNA) are reported. As expected, the Pyr ligand slows DNA binding by trans-[(H2O)(Pyr)(NH3)4RuII]2+ relative to [(H2O)(NH3)5RuII]2+ and favors reduction of RuIII by about 150 mV. The pyridine ligand also promotes the disproportionation of RuIII to afford the corresponding complexes of RuII and, presumably, RuIV. For L = Ino, disproportionation follows the rate law: d[RuII]/dt = k0[RuIII] + k1[OH-][RuIII], k0 = (2.7 +/- 0.7) x 10(-4) s-1 and k1 = 70 +/- 1 M-1 s-1.