Fourteen patients with transitional cell carcinoma of the urinary bladder were treated with 4,000 cGy of pelvic irradiation concurrent with two 96-hour infusions of 5-fluorouracil (5-FU). Three weeks after completion of this regimen, patients underwent repeat cystoscopy and deep-muscle biopsy at the site of their original neoplasms. Eight of 14 (57%) had no tumor left in the biopsy specimen, and they received an additional course of chemotherapy and radiation therapy to a total dose of 4,400 cGy to the pelvis and 6,000 cGy to the bladder. Five of the 14 had residual tumor in the biopsy specimen (one did not undergo biopsy) and went on to planned cystectomy. Two of the five had no tumor in the cystectomy specimen. Overall, ten of the 14 patients (71%) have been downstaged to a condition of P0 (no tumor) following 4,000 cGy and two courses of 5-FU. Of eight patients with retained bladders, seven remain well at a median follow-up of 7 months. At a range of follow-up of 3-21 months and a median of 7 months, 13 of 14 patients remain tumor-free. This regimen results in a greater percentage of downstaging than conventional irradiation alone, and may allow bladder preservation for those with radiation therapy- and chemotherapy-responsive tumors.