Time-resolved infrared difference spectra have been acquired for a series of Re(I) complexes by step-scan Fourier transform infrared spectroscopy, the first application of the step-scan technique to transient inorganic photochemistry. Shifts in v(CO) following laser flash excitation at 354.7 nm in CH3CN at room temperature show that the lowest-lying excited state in fac-[Re(phen)(CO)(3)(4-Mepy)](+) (1) is a metal-to-ligand charge transfer (MLCT) state, in fac-[Re(dppz)(CO)(3)(PPh(3))](+) (2) a (3) pi pi* state, and in fac-[Re(4,4’-(NH2)(2)bpy)(CO)(3)(4-Etpy)](+) (3) a mixture of ligand-based and MLCT states.