In situ diffraction experiments were performed with high-energy synchrotron X-rays to examine load partitioning and high-stress relaxation during uniaxial compression of a bulk metallic glass composite containing both ductile tantalum particles and crystallized matrix material. The tantalum particles yielded at an applied stress of -800 MPa, while the matrix precipitates remained elastic up to the maximum applied stress of -1250 MPa. The von Mises effective stress in the tantalum particles at yielding was 1500 MPa, well in excess of typical tantalum yield stresses, which is attributed to a combination of solid-solution strengthening and the inhibition of dislocation motion in the 1-2 mum particles. A series of constant crosshead-position measurements made at -1250 MPa suggested the possibility of room-temperature matrix relaxation under high applied loads. (C) 2003 Elsevier Science B.V. All rights reserved.