Materials from joint endoprothesis are the source for particle induced reactions in the SLIM (Synovia Like Interface Mem- brane) which are relevant for endoprosthetic pathologies especially in aseptic prosthesis loosening. The identification of wear particles in the SLIM is due to the heterogeneity of implant materials, due to the complexity of particle genesis and its differential diagnosis to non prosthesis-material particles a great challenge for histopathologists. This “particle algorithm” is based on 1) conventional transmitted light microscopy with a guide to sizing, shaping and coloring 2) polarization optical criteria and 3) enzyme-histochemical properties (oil red O staining and Prussian blue reaction). Based on these criterias the complete spectrum of particles in the SLIM may be defined including non-ferrous metals and metal alloys, ferrous metals, wear particle corrosion, ceramic particles, bone cement (polymethyl methacrylate, PMMA) particles, PMMA additives such as X-ray contrast medium (zirconium dioxide or barium sulfate), and non-metallic and non-ceramic materials (polyethylene particles, carbon particles, silicon). The most relevant non prosthesis-material particles include calciumpyrophosphate, urate, calciumcarbonates and hemosiderin. Since in principle all wear particles may exert inflammatory or immunological properties, the diagnosis of particle induced inflammatory or immunological reactions should be carried out in the context of the Consensus-Classification of the SLIM leading to a definite SLIM type classification. In respect of the particle heterogeneity an open web based “particle algorithme” would be helpful which could include all material particles in a rapid changing field of material science. For histopathological diagnosis a “particle score” for the SLIM is recommended evaluating 1) the predominant prosthesis-material particle type in respect to micro-, and macroparticles, 2) the existence of non prosthesis-material particles and 3) the quantification of particle induced necrosis and lymphocytosis.