The European Organization for Research and Treatment of Cancer genitourinary group has completed 2 parallel prospective randomized studies, one with 30 mg. mitomycin C and the other with 50 mg. doxorubicin as adjuvant intravesical treatment after transurethral resection of superficial transitional cell bladder carcinoma. These studies were designed to compare early (the day of resection) versus delayed (between 7 and 15 days after resection) instillations and short-term (6 months) versus long-term (12 months) treatment. The results indicate that in regard to recurrence rate patients having a delayed and short-term treatment do worse than those having early instillations (for 6 or 12 months) or those having prolonged treatment (either immediate or delayed). With an average followup of 4 years survival, progression beyond T1 disease, development of distant metastases and appearance of a second primary were not influenced by the therapeutic regimen. A multivariate analysis of prognostic factors is presented, which indicates that after adjustment for these factors, patients in the delay, no maintenance arm have a significantly higher recurrence rate than the other patients.