Fluorescein, eosin Y, and rose bengal are dyes used in clinical medicine and considered (photo-)chemically stable. Upon extensive irradiation with visible light in aqueous solutions, we found that these compounds release carbon monoxide (CO) – a bioactive gasotransmitter – in 40–100% yields along with the production of low-mass secondary photoproducts, such as phthalic and formic acids, in a multistep degradation process. Such photochemistry should be considered in applications of these dyes, and they could also be utilized as visible-light activatable CO-releasing molecules (photoCORMs) with biological implications.