Rate constants for outer-sphere cross-reactions of the couples Ru/sub 2/(NH/sub 3/)/sub 10/pz/sup 6+/5+/ (pz = pyrazine), Ru/sub 2/(NH/sub 3/)/sub 10/pz/sup 5+/4+/, RuRh(NH/sub 3/)/sub 10/pz/sup 6+/5+/, Ru(NH/sub 3/)/sub 5/pz/sup 3+/2+/, and Ru(NH/sub 3/)/sub 5/pzCH/sub 3//sup 4+/3+/ (pzCH/sub 3/ = methylpyrazinium) with the couples Ru-(NH/sub 3/)/sub 5/py/sup 3+/2+/ (py = pyridine), Ru(NH/sub 3/)/sub 4/(bpy)/sup 3+/2+/ (bpy = 2,2'-bipyridine), and Co(bpy)/sub 3//sup 3+/2+/ have been measured at 25/sup 0/C and ionic strength 0.10 M (trifluoromethanesulfonate). The rate constants for the Ru(NH/sub 3/)/sub 5/py/sup 3+/2+/ and Ru-(NH/sub 3/)/sub 4/bpy/sup 3+/2+/ reactions were treated according to the electrostatically corrected, adiabatic Marcus equation and yielded the following estimates of the rate constants for self-exchange reactions (in the same order as above): 15, 6.7 x 10/sup 3/, 9.0, 1.4 x 10/sup 4/, and 39 M/sup -1/s/sup -1/. The trends are discussed on the basis of inner-sphere and outer-sphere reorganization energies. The cross-reactions of the Co(bpy)/sub 3//sup 3+/2+/ couple appear to be mildly nonadiabatic.