Abstract: Two palladium arsenide-antimonides have been found as small inclusions associated with native gold at Hope's Nose. One of the minerals has been identified as isomertieite; the other is chemically very similar to mertieite-II (Cabri et al., 1975). Electron probe microanalysis gives the formula of the isomertieite as (Pd10.89 Au0.08Cu0.03)Σ11.00(Sb2.01As1.99)Σ4.00 and of mertieite II as (Pd7.90Au0.07Cu0.01)Σ7.98(Sb2.43As0.59)Σ3.02. The relectance spectra of isomertieite in air and in oil at intervals of 10 nm from 400–700 nm are tabulated. The luminance values of the Hope's Nose isomertieite are 55.5 % in air and 42.5% in oil. The type specimen of isomertieite from Itabira, Minas Gerais, Brazil, has been re-examined; a new electron probe analysis is given and improved reflectance spectra are tabulated. The latter gives luminance values of 54.3% in air and 41.3% in oil.