Photoactivated carbon monoxide (CO) release by the iron carbonyl complex [Fe-II(CO)(N4Py)](ClO4)(2) (1) is described. Compound 1 is a low-spin ferrous complex the is highly stable and soluble in aerobic aqueous solutions. CO release was studied by the substitution of MeCN for CO, which displays saturation kinetics, and by the transfer of CO to deoxymyoglobin, which is slow in the dark but fast upon irradiation with UV light (365 nm). Compound I is active against PC-3 prostate cancer cells and shows potent photoinduced cytotoxicity. In addition, the iron carbonyl complex was attached to a short peptide toward the goal of tissue or cell-specific delivery.