Exposure of male Charles River CDI rats to a 5% saccharin diet in utero and throughout weaning, conditions associated with tumor induction, did not induce detectable metabolism (less than 0.4% of the oral dose) of tritiated saccharin in vivo. No metabolites (less than 0.06 microgram per kilogram per 24 hours) were detected in the urine of normal rats given a tracer dose. Pretreatment with 3-methylcholanthrene did not induce saccharin metabolism.