Patients with transitional cell carcinoma of the bladder treated by radical megavoltage X ray therapy are analyzed. There was a significant correlation between tumor T stage classification and the hemoglobin level at the start of radical radiotherapy. A hemoglobin level of 12g/dl or more was associated with a significant improvement in complete local tumor regression at 6 months and durable local tumor control for patients with T3 cancer or a cancer of grade 3 histology. Hemoglobin level did not influence survival for patients with T1 or grade 1 cancer. Those patients with T2-T4 cancer, grade 2-3 cancer, or a cancer of solid or mixed appearance had a significantly better survival probability if their hemoglobin level was more than 13g/dl. Hemoglobin level would appear to exert its influence on survival by an effect on local tumor control. It has no significant independent effect on the hazard of distant metastases.