Flow cytofluorometry and drug targeting with labelled neoglycoproteins are used as tools to probe for membrane lectins in two human adenocarcinoma cell lines. Both cell lines express activities for galactosides, glucosides and fucosides. Affinity chromatography on gels with immobilized sugar leads to purification of an alpha-galactoside-binding protein at an apparent molecular weight of 64 kDa that also binds to lactose, maltose and fucose and exhibits Ca2+-requirement for binding, a beta-galactoside-binding protein without Ca2+-requirement at an apparent molecular weight of 14 kDa, and an alpha-glucosyl-binding protein without Ca2+-requirement at an apparent molecular weight of 34 kDa from both cell lines. The description of membrane lectins, documented here for the first human tumor cell lines, is an initial step towards a lectin-based improvement of the clinical management of human colon adenocarcinoma.