The study attempted to define characteristics of renal podocytes in nephrotic syndrome glomerulopathies in children with and without glomerular immaturity based on the histochemical expression of cytokeratin 18 (CK 18) and vimentin. Material consisted of 29 renal biopsies performed in the Department of Pediatric Nephrology, Poznan University of Medical Sciences, between 1991 and 2000. The study group included 16 children with mesangial glomerulonephritis (MesGN) and signs of glomerular immaturity and 13 children with MesGN without signs of glomerular immaturity. The control tissue was derived from macroscopically normal renal cortex taken from kidneys resected for localised neoplasms ( n=3). In the control samples, the immunocytochemical expression of CK 18 was found only in epithelial cells of proximal and distal tubules. Vimentin was present in all podocytes, some mesangial cells and endothelium. In all cases of children with MesGN with signs of immaturity, both CK 18-positive and vimentin-positive podocytes were found. In all cases of MesGN without immaturity we revealed CK 18-negative podocytes but with distinct vimentin-positive expression. Reorganisation of cytoskeletal proteins within immature podocytes may be associated with the unfavourable clinical course of nephrotic syndrome in children. The application of antibodies against intermediate filaments may help to differentiate between mature and immature forms of MesGN.