During the last 10 years, there have been many major advances in our understanding of the pathogenesis of glomerular injury. Of particular significance has been the recognition of the importance of proteolytic enzymes and oxidants in mediating glomerular capillary wall and mesangial damage. The infiltrating polymorphonuclear leukocyte (neutrophil, PMN) and monocyte have been long recognized as important sources of proteinases and reactive oxygen species [reviewed in 1–3]. However, it is now known that endogenous glomerular cells may also release proteinases and oxidants that may also influence the local inflammatory response [reviewed in 4–8]. In this brief review, we will highlight some of the studies from our laboratory that have dealt with these important mediators. For a more comprehensive discussion of the role of proteinases and reactive oxygen species in glomerulonephritis (GN), the reader is referred to several excellent reviews [4–8].