Despite the apparent and well-known toxic effects of carbon monoxide (CO), studies on the intriguing biological roles of this molecule are rapidly emerging. Recent investigations have brought to the limelight various physiological effects of CO which include, among others, vasorelaxation and inhibition of organ rejection after transplantation. The importance of CO in biology can be compared with another gas, nitric oxide (NO), an essential and ubiquitous signalling molecule. This parallelism led to the tantalising concept of using CO for therapeutic purposes wherein compounds that transport and deliver this gas to a target tissue would clearly facilitate both the clinical feasibility and the specificity of CO therapy. Sodium boranocarbonate, Na[H3 BCO2H] (1) was the first water-soluble and non-transition metal containing CO-releasing molecule (CO-RM) to be identified. In order to tune the rate of CO release, we modified 1 and synthesised and characterized various derivatives which release CO under physiological conditions but at rates different from the parent compound 1. The synthesis, structure and CO-releasing properties of ester and amide derivatives of 1 will be presented together with some biological studies carried out with a selection of the compounds.