Cell surface expressed lactosaminyl glycans were determined on live cells by flow cytometry using a sialyltransferase mediated labeling procedure. Fluorescent CMP-sialic acid and Galβ1,4GlcNAc α2,6-sialyltransferase were applied to probe expression of acceptor glycans on untreated or sialidase pretreated erythrocytes. After enzymatic fluorescence labeling, erythrocytes were treated with endo-β-galactosidase or trypsin to distinguish polylactosaminyl- and complex-type glycans. The expression of lactosaminyl sequences on cord- was 20% lower than on adult cells. After sialidase treatment fluorescence incorporation on both cell types increased twofold compared to untreated cells indicating a low sialylation extent. A recombinant α2,3-sialyltransferase was preferentially labeling polylactosaminyl glycans. Taking advantage of the different fine specificity as determined here, α2,6- and α2,3-sialyltransferase can be applied to distinguish certain types of lactosaminyl glycans.