1. The senior author's personal experiences in the treatment of transitional cell carcinoma of the bladder with supervolt therapy since 1939 are reviewed with respect to curative results and late function of the bladder. The material includes the observations at the Tumor Institute of the Swedish Hospital, Seattle, and in the Section of Therapeutic Radiology of the University of California in San Francisco. 2. The technique consisted mainly of 3 stationary fields, using 8oo kv., 1 mev., 2 mev., and cobalt 60 radiation. The doses delivered to the bladder in the Seattle series were around 4,500 to 5,000 r in 35 to 45 days, in the San Francisco material, 5,500 to 6,000 r in 5½ to 7 weeks. 3. Five-year "cures" by one course of radical radiation therapy were accomplished in the Seattle material in 14 of 85 patients (16 per cent), 10 year cures in 9 of 66 patients (13 per cent). In the San Francisco experience, the 5 year cure rate was 4 of 29, or 14 per cent. "Cure" means cystoscopically and functionally normal bladder without recurrence at any time. 4. In all of those patients treated since 1939 who remained cured over periods of up to 22 years, the bladder function was entirely normal. Fibrosis in this material was observed in only 1 patient who received 7,500 r bladder dose. In the material treated before 1939, following excessive doses during the early years of the use of supervolt therapy, some severe late pelvic damage was observed. From this material and from reports in the literature6 it appears that a 6,000 to, at most, 6,500 r bladder dose (with fractionation of 900 to, at most, 1,000 r per week) is the limit of consistent tolerance of the bladder. 5. Suitable for radical external irradiation are 2 types of transitional cell carcinoma: very undifferentiated carcinomas (Grade IV) regardless of the pelvic extent, and carcinomas, Grades II and III, prior to invasion, or at least prior to massive invasion, of the muscle. The author's present policy in the treatment of solitary lesions of Grade II and III consists, therefore, in recourse to radical radiation therapy after the first recurrence following thorough transurethral resection. In the presence of multiple lesions at first cystoscopy, primary radiation therapy is recommended. In Grade IV carcinoma, radiation therapy is the immediate method of choice.