There is no body cancer which is as well adapted for attack by radon implants as bladder carcinomas. Notwithstanding that these tumors are radioinsensitive, their accessibility to cystoscopic view and suprapubic exposure, their long confinement to the bladder, the flexibility of radon seed implantation and the possibility of early diagnosis all contribute to place bladder cancers in a unique class for control by radon implants. Cystoscopy in a fourth of all cases offers a means of both seeing and implanting the entire tumor. Because of size, position or bleeding, three fourths of all bladder cancers have to be subjected to suprapubic cystotomy, both to view completely and implant accurately the tumor with radon seeds. Such an operation has a relatively low mortality; 5 per cent as top, 3 per cent as low, if cases are carefully worked up. Papillary cancers of the bladder are confined to the bladder for a