Eleven patients were entered in a phase I/II study to evaluate the toxicity and effectiveness of the use of misonidazole with radiation in cancer of the bladder. The radiation fractionization used is shown in Figure 1. Misonidazole was administered in a dose of 1.5 g/m2, 4-6 hours before the radiation dose. The large radiation dose (400 rad) used with misonidazole was designed to obtain maximum enhancement of radiation sensitizer effect. Only minor misonidazole toxicity was observed. Tumor regression was dramatic, with 7/9 patients achieving complete regression of disease. Three patients however, developed severe small bowel complications, probably from the unconventional radiation fractionation used. In view of this high complication rate, this study was terminated.