Rats given oral doses of [3-14C] saccharin excreted 56-87% of the labeled dose in the urine and 10-40% in the feces during 7 days. Distribution studies showed that the highest levels of 14C were in the kidneys and bladders. The bile was not a significant route of excretion. The presence of labeled CO2 in expired air indicated that saccharin was decarbosylated to a slight degree. DEAE chromatographic separation and isolation of labeled compounds from urine samples showed that more than 99% of the urinary 14C was unchanged saccharin. Up to 1.0% of the 14C was a metabolite identified as 0-sulfamoylbenzoic acid. Comparative metabolic profiles of a dog, rabbit, guinea pig and hamster indicated that there was little difference in the pattern due to animal species or dose level.