The reaction of molecular hydrogen with HOs3(CO)10(NO) leading to the reduction of the nitrosyl ligand has been studied. Four products have been isolated and a reasonable mass balance of osmium has been obtained. Two of the products, H2Os3(NH)(CO)9 and the unusual hydrogen-rich cluster H4Os3(NH)(CO)8 are new, and spectroscopic data for their formulations and proposed structures are presented. The other two products, HOs3(NH2)(CO)10 and H4Os4(CO)12, have been previously characterized. A new route to HOs3(NH2)(CO)10 starting from the triazenido cluster, HOs3(HN3H)(CO)10, has also been studied. Interconversions between the imido and amido clusters were investigated.