Cytokeratin 7 was found to occur in the columnar and glandular epithelium of the lung, cervix, breast, bile ducts, larger collecting ducts of the kidney and in mesothelium, but is absent from gastrointestinal epithelium, hepatocytes and myoepithelium. Several types of adenocarcinomas of the gastrointestinal tract and of the urinary tract are negative, while adenocarcinomas of the mammary gland, ovary and lung are positive.