Bulk metallic glasses (BMGs) possess a unique set of mechanical properties that make them attractive structural materials. However. when loaded without constraint, BMGs fracture catastrophically due to formation of macroscopic shear bands and this behavior reduces their reliability. To address this issue, BMG matrix composites have been developed. In this investigation. neutron diffraction was used during uniaxial compressive loading to measure the internal strains in the second phases of various BMG composites reinforced with Ta, Mo. or stainless steel wires. The diffraction data were then employed to develop a finite element model that deduced the in situ constitutive behavior of each phase. It was found that the reinforcements yielded first and started transferring load to the matrix. which remained elastic during the whole experiment. While the present composites exhibited enhanced ductility. largely due to their ductile reinforcements. they yielded at applied stresses lower than those found in W reinforced composites. (c) 2005 Elsevier B.V. All rights reserved.