Uniaxial tension tests were performed on standardized specimens of bovine haversian bone to examine the contributions of mineral and collagen to permanent deformation in bone and to monitor the damage mechanisms occurring in permanent deformation using acoustic emission techniques. Test on control, decalcified and deproteinized groups of specimens demonstrated that the post-yield or ‘plastic’ slope of the stress-strain curve for unaltered bone is dependent on collagen properties, while the elastic modulus and yield phenomenon appear more dependent on the mineral phase. The results are consistent with a two-phase model for bone in which the mineral behaves as an elastic-perfectly plastic material when bound to the collagen fiber matrix. Acoustic emission from control specimens demonstrated considerable damage at yield and again just prior to fracture. Decalcified specimens, which were linearly elastic to failure, also exhibited significant acoustic emission just prior to fracture.