Metal-nitrosyls are assumed to be intermediates in catalytic converters, which reduce the emission of  from internal combustion engines.  This application has been described as "one of the most successful stories in the development of catalysts."
Metal-catalyzed reactions of NO are not often useful in organic chemistry. In biology and medicine, nitric oxide is however an important signalling molecule in nature and this fact is the basis of the most important applications of metal nitrosyls. The nitroprusside anion, [Fe(CN)NO], a mixed nitrosyl cyano complex, has pharmaceutical applications as a slow release agent for NO.  The signalling function of NO is effected via its complexation to haeme proteins, where it binds in the bent geometry. Nitric oxide also attacks iron-sulfur proteins giving dinitrosyl iron complexes.