Elderly patients with nonoperable transitional cell carcinoma of the bladder need a rather active, but less toxic treatment than full-dose polychemotherapy. This study was designed to determine whether the cisplatin-analogue carboplatin (which is less nephrotoxic and less neurotoxic than the parent compound) has sufficient activity against T2-T4 neoplasms (both nonmetastatic and metastatic) to warrant further development in phase III trials. Carboplatin dose was adjusted according to creatinine clearance, with a maximum dose of 300 mg/m2. The patient selection for this screening for activity was adjusted by the use of the 'optimal' two-stage design. Seventeen patients were enrolled, with a median age of 78 years (range: 70-85), a median performance status of 80% (range: 70-90%); 13 patients were lymph node-negative (10 T2, 2 T3, 1 T4) and 4 had locoregional or distant node metastases. Nine patients had a complete response (3 in the first, 9-patient, stage, and 6 in the second, 8-patient, stage), demonstrating that carboplatin had sufficient activity (at the 'desirable' target level of 35%); almost all responses were observed in T2 patients. Six patients had stable disease, and 2 had disease progression during treatment. The toxicity was acceptable, with only 41% of patients having grade II-III hematologic toxicity. More than 30% of patients were estimated to be free from progressive disease (54% alive) at 24 months. In our opinion carboplatin is suitable to be tested-in a phase III testing versus full-dose radiation therapy-as adjuvant after initial transurethral resection of the prostate in elderly patients with T2 transitional cell carcinoma of the bladder considered radically nonoperable for medical problems.