We studied peanut lectin (PNA) binding sites in human fetal colons (9 to 19 weeks' gestational age). Peanut lectin has a specificity for beta-D-galactose(1--3)N-acetyl-D-galactosamine (beta-D-Gal [1----3]-D-GalNac) that is the purported determinant for the T-blood-group antigen (TAg) and a precursor of MN-blood-group substance, lacking only in a terminal sialic acid. In the normal adult human colon, PNA fails to bind to the actual goblet theca but does have binding sites localized to the supranuclear portion of both columnar and goblet cells. This represents the detection of nascent oligosaccharides prior to addition of terminal sialic acid. Neuraminidase treatment of adult colons localized PNA to the goblet theca itself and to the apical and/or glycocalyx region of columnar cells. Fetal colons localized PNA to the region of the glycocalyx of columnar cells while the goblet theca itself failed to express PNA binding sites. After treatment of fetal colon sections with neuraminidase, PNA binding was noted in the goblet theca itself. Goblet cells of the human fetal colon exhibit a PNA binding pattern somewhat similar to adult goblets; however, fetal columnar cells have a PNA binding pattern as reported in colonic adenocarcinomas. This pattern of complete and incomplete synthesis of MN-blood-group substances in goblet and columnar cells, respectively, has also been demonstrated in adenomas of the human colon.