In order to investigate the malignant potential of stage T1 bladdar tumors the status of p53 overexpression and mucosal change of grossly normal bladder mucosa, respectively, were studied regarding tumor recurrence and tumor progresion. A total of 30 cases with stage T1 bladder tumor were enrolled and selected site mucosal biopsies (SSMB) were taken of randomly selected 17 cases. All cases were treated by transurethral resection and followed for a median period of 39 months. Six of the 30 cases (20%) showed p53 overexpression. Five of the 17 (29%) had mucosal changes (carcinoma in situ