Human colonic adenocarcinoma tissue and derived cell lines have been characterized by an abundance of different type 1 and 2 lacto series glycolipid antigens which are either low or not found in normal colonic mucosa. The enzymatic basis for the expression of contrasting glycolipid compositions between adenocarcinomas and normal colonic mucosa, as well as between derived cell lines, has been studied. The following results were of particular interest. (i) Abundant activities of beta 1—4galactosyltransferase associated with synthesis of both lactosylceramide and lactoneotetraosylceramide, beta 1—3galactosyltransferase for synthesis of lactotetraosylceramide, and an alpha 1—3/4fucosyltransferase responsible for synthesis of Lex and Lea antigens were found in normal colonic mucosa or in a normal mucosal epithelial cell line HCMC, or in both. Variable levels of these activities were found in adenocarcinoma tissues and in various established adenocarcinoma cell lines. In striking contrast, significant activity of a beta 1—3N-acetylglucosaminyltransferase responsible for synthesis of lactotriaosylceramide (Lc3) was found in various cases of colonic adenocarcinoma and cell lines, but was undetectable in normal colonic epithelial cells. (ii) In situ transfer of galactose to Lc3 was performed on histologic sections by preincubation of the tissue with acceptor glycolipid followed by incubation with UDP-galactose. The biosynthesized glycolipid was revealed by indirect immunofluorescence with the monoclonal antibody 1B2 which defines lactoneotetraosylceramide antigen. In these studies, histologic sections prepared from frozen normal proximal colon tissue were shown to lack native type 2 chain structures. However, transfer of galactose from UDP-galactose could be demonstrated in the epithelial cells of normal proximal colon after incorporation of Lc3 into the membranes, indicating the ability of normal colonic epithelial cells to synthesize type 2 chain core structures if the precursor Lc3 is available. In contrast, adenocarcinoma tissues showed significant native immunofluorescence with the antibody. These data suggest that an accumulation of both type 1 and 2 chain lacto series glycolipids with alpha 1—3- or alpha 1—4fucosyl substitution in human adenocarcinoma is due to enhanced beta 1—3N-acetylglucosaminyltransferase rather than enhancement of other enzymes. This enzyme may play a key role in regulating the level of various types of lacto series tumor-associated antigens with the lacto type 1 or 2 chain.