Established in 1974 from the second in a series of 3 primary colonic tumours resected from a 65 year old Caucasian female, which was classified as a Duke's B mucin producing colon adenocarcinoma. LS 123 is aneuploid, fails to grow progressively in nude mice and forms colonies only in enriched semisolid medium developed for tumour stem cells. The cells will grow in either low serum or serum free medium. In chick embryonic skin assays the cells grow as a well differentiated abnormal colonic epithelium with little mitotic activity and low invasiveness. LS 123 exhibits several properties associated with neoplasia, but have little invasive potential and may represent an early stage in tumour development.