Various compounds were screened for antipromoter activity in bladder carcinogenesis in rats with a view to using them clinically to inhibit postoperative intravesical ectopic tumor growth of superficial papillary bladder cancer. Their inhibitions of the effect of sodium saccharin in maintaining increased agglutinability of bladder cells by concanavalin A were examined in 4-week tests. The compounds found to inhibit the effect of saccharin were alpha-tocopherol, ascorbic acid, aspirin, all-trans aromatic retinoid, alpha-difluoromethylornithine, sodium cyanate and p,p'-diamino-diphenylmethane. Considering the toxicities of some of these chemicals, ascorbic acid and alpha-difluoromethylornithine were concluded to be the most promising for future clinical trials.