Abstract: Beverages are provided and administered for producing LIS samples containing cells exfoliated from throughout the gut in sufficient numbers and free of interfering substances such as formed fecal particles for chemical assays and biologic assays for nucleic acid sequence information, and medical diagnosis. A kit is also provided for use by patients without assistance to produce a LIS sample suitable for analysis. A collection kit employs a sequence of the beverages and other ingested substances to produce preserved cells for medical diagnosis, allowing cytologic analysis of the LIS for diagnosis of foregut and hindgut disease. A preliminary cathartic lavage is used to cleanse a patient's digestive tract; at least one stool induced by the preliminary cathartic lavage is collected; and a final cathartic lavage is used to exfoliate and preserve cells from a patient's digestive tract.