Saccharin, first synthesized in 1879 by Fahlberg, has been used as a non-caloric sweetener with several advantages. It is sweet, non-caloric, and stable, can now be synthesized with relatively few impurities, and is inexpensive. Its toxicity, imagined and real, has long been a source of concern and debate. Intensive studies on the potential carcinogenicity of saccharin have been performed, extending the limits of our technology to evaluate carcinogenic risk of chemicals. Saccharin has been found to be a carcinogen only in rats and only if administered over two generations. The effect seems to be directed primarily to the lower urinary tract and is greater in males than in females. Also, saccharin has been found to enhance or promote the carcinogenic process in rat models. The form of saccharin administered in the diet or drinking water has been the sodium salt. No effects have been found with acid saccharin. Epidemiological studies in human beings have not found an increased risk of developing bladder cancer with exposure to saccharin.