The microstructure and chemistry of macroparticles in CrN films prepared by an arc ion-plating method on AISI 304 stainless steel was characterized by an energy filtering transmission electron microscope (TEM) equipped with an electron energy loss spectroscopy (EELS) detector. The surface morphology of the CrN coatings with macroparticles was examined by a high-resolution field emission scanning electron microscope (SEM). SEM observation shows that the macroparticles lie on craters and protrude out of the coating surface. Cross-sectional and plan-view TEM results reveal that the macroparticles are bud shape, which has the Cr metal located at the bottom center and surrounded by a chromium nitride layer. Quantitative EELS analysis of a macroparticle from the core region to the outer shell shows that the nitrogen and oxygen concentrations in the macroparticle increase from 17.7 to 38 atom % and 7.7 to 9.5 atom %, respectively. On the basis of the analysis, a model describing the formation of macroparticles in the arc ion-plated CrN coatings is proposed. (C) 2003 The Electrochemical Society.