Adequate data on the carcinogenicity of saccharin and cyclamate to humans are available only for the urinary bladder. In the studies available, exposure to saccharin and to cyclamate cannot be distinguished readily. Descriptive studies have shown no evidence of time trends in bladder cancer that can be related to use of saccharin or cyclamate. Likewise, studies of diabetics, who have used more saccharin and cyclamate than other people, have shown no evidence of an increased risk of bladder cancer. This association, however, is probably confounded negatively by cigarette smoking. Thirteen case-control studies have addressed the relationship of saccharin and cyclamate intake to bladder cancer in individuals. While statistically significant positive associations have been observed, a similar number of significant negative associations has also been observed. Studies of the dose-response relationships have also shown no consistent pattern. Studies of saccharin and cyclamate use with smoking habits have shown no consistent interaction with heavy smoking, as might be expected from a promotional effect. In some studies, however, an increased risk with saccharin and cyclamate use has been observed in female non-smokers--a group otherwise at low risk for bladder cancer.