Considering the interest of one of our groups for the investigation of Ru(II) complexes with various ligands resulting in versatile types of biological activities (antitumour, antibacterial, enzyme inhibitory, etc.)19,20, we report in this communication the preparation and investigation as CA inhibitors of organoruthenium(II) complexes of acetazolamide, which were found to possess subnanomolar affinity for many pharmacologically relevant isoforms, such as the cytosolic CA I and II and the transmembrane, tumour-associated CA IX and XII. This evidence concerns the gene CA9 and neoplasm.