In-utero or immediate post-utero exposure of rats to saccharin results in an increased incidence of bladder tumors when compared to post-weaning exposure only. We studied 6 human mother-infant pairs following maternal intake of saccharin close to delivery. High performance liquid chromatography revealed the presence of saccharin in all 6 newborn cord sera as well as their mothers' sera and urine. This constitutes the first report of placental transfer of saccharin in humans. Despite the relative weakness in carcinogenicity of saccharin, this in-utero exposure, coupled with ex-utero exposure, may possibly contribute to an increased incidence of neoplasms.