Analysis of glomerular anionic charge in human renal biopsy specimens has been restricted previously to staining of sites at the electron microscopic level, which is a product that needs skills and precludes a wide observable area. The introduction of a new tool, confocal laser scanning microscopy together with FITC conjugated poly-L-lysine as a cationic tracer, which demonstrates fixed anionic sites in thin sections from routinely formalin-fixed and paraffin-embedded renal biopsy tissue, has now enabled glomerular charge at light microscopic level. In this method, the patterns of staining in tissue showing minimal change nephrotic syndrome (MCNS) indicate that the intensity of anionic charge in 4 children with heavy proteinuria was significantly less than that in 7 children without proteinuria at remission, supporting previous observations using electron microscopy. Furthermore, staining the serial sections after methylation or saponification revealed that carboxyl components such as sialic acid may be responsible for proteinuria. We anticipate that this method may facilitate the investigation of the participation of charged components in the pathogenesis of MCNS and their role in relation to glomerular proteinuria.