The high-rate fracture behaviour of two hybrid, particulate, composite systems consisting of a polypropylene matrix, containing both inclusions of ethylene-propylene rubber and particles of talc or calcium carbonate, was investigated by varying the formulation of the dispersed phase. Depending on the behaviour of the different materials, linear elastic or elasto-plastic fracture mechanics was applied to determine their fracture resistance. It was found that, for certain compositions, the hybridization of the secondary phase produces synergistic effects with respect to the corresponding binary systems.