We report the synthesis of nitric oxide-releasing gold nanoparticles formed by place-exchange reaction of hexanethiol monolayer-protected clusters with diamine nitric oxide donor precursor molecules, which are subsequently converted to N-diazeniumdiolate NO donors. The nitric oxide release from the N-diazeniumdiolate-modified gold nanoparticles is tunable by varying the number and/or the chemical structure of the exchanged amine ligands. The size and stability of NO-releasing nanoparticles may prove useful for a range of biomedical and pharmaceutical applications.