Urinary oligosaccharides from nephrotic syndrome patients were investigated by Bio-Gel P-4 column chromatography and methylation analysis to clarify the electrostatic defects and size barrier defects in the glomerular basement membrane of nephrotic syndrome patients. The levels of urinary oligosaccharides (nmol/mg creatinine) in nephrotic syndrome patients were about 25 times the levels in controls. The ratio of neutral oligosaccharides to sialyl oligosaccharides was about 1:1 in the urine of nephrotic syndrome patients. The levels of neutral oligosaccharides in the urine of nephrotic syndrome patients were about 13 times that of controls. The proportion of trisialylated oligosaccharides in the urine of nephrotic syndrome patients was higher than that in galactosialidosis patients. These findings suggest that electrostatic defects and size barrier defects in the glomerular basement membrane might contribute to the characteristic oligosacchariduria of nephrotic syndrome patients. In addition, the structures of 11 different kinds of oligosaccharides that have not been previously reported were identified in the urine of nephrotic syndrome patients.