Mucins derived from colonic cancers differ immunologically and chemically from those in normal colonic epithelium. It has been demonstrated that the lectin from the peanut will bind to mucins present in colonic cancers and other neoplastic lesions but not to those from the normal colon. It was hypothesized, therefore, that in transformed colonic epithelium the glycosylation of mucins occurs differently than in normal epithelium. To rule out the possibility that the differences in oligosaccharide structure were due to postsecretory degradation, studies were designed to evaluate cancer-associated colonic mucins produced under more controlled conditions. We studied nine different cancer cell lines first in monolayer culture and then as xenografts in athymic or nude mice. Eight of the nine cell lines in monolayer culture synthesized glycoconjugates that were labeled by fluorescein-conjugated lectins. After injection into nude mice, eight of the nine cell lines produced tumors typical of human colonic cancer, and six of nine secreted mucin. The mucins produced by the xenografts were labeled at fluorescence microscopy by peanut lectin and other lectins, characteristic of what had been seen in other primary human colonic cancers. One cell line, LS174T, produced large amounts of mucin in the xenograft model. Mucin was purified from these tumors and characterized biochemically. It was demonstrated that mucin purified from the xenografts bound peanut lectin. Therefore, we have concluded that cancer-associated mucins are present in cultured colorectal tumor cells. The cancer-associated mucins are also found in nude mouse xenografts, indicating that they are not the result of postsecretory degradation by colonic flora or by tumor cell necrosis. The cell culture and xenograft can therefore be useful for studying the biosynthesis of cancer-associated mucins.