The effects of solvent composition on the lifetimes and intersystem crossing efficiencies of Cr(CN)63- and Co(CN)63- have been determined for polyalcohol-water mixtures. The Cr(CN)63- lifetime varies from 0.12 μs in H2O to 0.94 μs in glycerol-water (XH2O = 0.31), while the Co(CN)63- lifetime changes from 2.6 to 4.7 ns. Refractive index corrections can substantially affect the apparent intersystem crossing efficiencies, but, after correction for this artifact, intersystem crossing in both complexes changes only slightly, if at all, with solvent composition. © 1979 American Chemical Society.