Abstract: The identification is disclosed of a new molecular factor for the early diagnosis of urothelial carcinoma of the bladder. HtrA1 is a molecule that is produced mainly by the urothelium of the bladder, both in physiological and inflammatory pathologies, such as cystitis, whereas it is absent in the urothelial layer of the neoplastic bladder mucosa, regardless of cancer grade and level. By means of Western Blotting two forms of HtrA1 were identified, both in bladder tissue and urine, the native 50 kDa form and the autocatalytic 38 kDa form. The 38 kDa form is significantly underexpressed in tumoral tissues compared with normal tissues and concentration of the 50 kDa form in urine is significantly higher in patients affected by bladder cancer compared to healthy subjects and subjects with cystitis. Therefore, the evaluation of tissutal and urinary HtrA1 levels can be a specific marker of urothelial carcinoma of the bladder.