A new group of CO-releasing molecules, CO-RMs, based on cyclopentadienyl iron carbonyls have been identified. X-Ray structures have been determined for [(η-C₅H₄CO₂Me)Fe(CO)₂X], X = Cl, Br, I, NO₃, CO₂Me, [(η-C₅H₄CO₂Me)Fe(CO)₂]₂, [(η-C₅H₄CO₂CH₂CH₂OH)Fe(CO)₂]₂ and [(η-C₅H₄CO₂Me)Fe(CO)₃][FeCl₄]. Half-lives for CO release, ¹H, ¹³C, and ¹⁷OC NMR and IR spectra have been determined along with some biological data for these compounds, [(η-C₅H₄CO₂CH₂CH₂OH)Fe(CO)₃]⁺ and [{η-C₅H₄(CH₂)_nCO₂Me}Fe(CO)₃]⁺, n = 1, 2. More specifically, cytotoxicity assays and inhibition of nitrite formation in stimulated RAW264.7 macrophages are reported for most of the compounds analyzed. [(η-C₅H₅)Fe(CO)₂X], X = Cl, Br, I, were also examined for comparison. Correlations between the half-lives for CO release and spectroscopic parameters are found within each group of compounds, but not between the groups.