This study presents the first in situ Os-isotopic compositions of distinct platinum-group mineral (PGM) assemblages from the metamorphosed chromitites of the Nurali ultramafic complex (Southern Urals, Russia). 'Primary'Ru-Os sulfides are commonly replaced by a'secondary'unnamed Ru-Os-Fe-lr oxide, providing evidence for different stages of desulfurization and oxidation of primary laurite (e. g., with relics of laurite or without laurite). The osmium isotope data define a restricted range of similarly'unradiogenic' 187Os/188Os values for 'primary' and 'secondary' PGM supporting the conclusion for closed system behaviour of the Re-Os isotope system during postmagmatic hydrothermal or metamorphic events. The Os-isotope data provide further support for an Enstatite Chondrite Reservoir (ECR) model for the convective upper mantle as defined by Walker et al. (2002).