The stroma of 509 epithelial tumors of the urinary bladder was examined. There was found a definite correlation between the stroma status, its histochemical properties and the histological structure of bladder tumor. During growth and malignant transformation the stroma and its histochemical pattern is significantly changed. The process of fibrosis develops with the accumulation of NMPS and decrease of AMPS as well as the reduction of argyrophil fibres characteristic of papilloma and differentiated transitional cell cancer. A predominance of argyrophil fibres with the accumulation of AMPS is typical for undifferentiated cancer which early infiltrates the organ wall and metastasize rapidly and extensively.