Recent studies on saccharin in animals and man have allowed a detailed understanding of its fate in the body. Saccharin is slowly absorbed from the gut but rapidly eliminated in the urine, largely by renal tubular secretion. Saccharin does not undergo detectable metabolism in either animals or man. Tissue specific accumulation in the urinary bladder, suggested by single and multiple dose studies in rats, was not found during chronic administration in the diet. The bladder tissue is part of the central, rapidly equilibrating, compartment. The sex- and generation-specificity of the tumorigenic effect is not due to unique accumulation in the urinary bladder of F1 males. Saturation of renal tubular secretion, which occurs in rats fed 5% saccharin or more in the diet, was not found in human volunteers given large oral doses (2 g).