Different ABS systems, produced by means of different polymerisation techniques (emulsion and mass polymerisations) and with different microstructural features were characterised and studied. Elastoplastic fracture mechanics tests were performed in order to compare the effects of the different morphologies of the dispersed phase on the mechanical responses. The plastic deformation mechanisms that give rise to energy dissipation were investigated in situ by means of transmission electron microscopy, and correlated to the observed fracture properties. information about the stress field around and inside the dispersed particles was also obtained by dynamic mechanical analysis. The microstructural characteristics of the materials account well for the performance differences : particles from emulsion polymerisation, in particular, can cavitate and then promote plastic deformation through shear yielding.