[formula: see text] A tight-binding, hydrophobic inhibitor of carbonic anhydrase II has been masked with a water-solubilizing, photolabile group derived from o-nitrophenylglycine. This caged inhibitor represents our first effort at the site-specific delivery of prodrugs that can be activated by light. Via this approach, we have begun to address the problems of water insolubility and systemic side effects on administration of tight-binding inhibitors of carbonic anhydrase.