The β(1–4)-linked oligosaccharides ofN-acetyl-d-glucosamine (GlcNAc) isolated from chitin were used to prepare synthetic immunogens and antigens by reductive amination of (GicNAc)n to bovine serum albumin (BSA). The rabbit antisera produced to the (GlcNAc)n-BSA conjugates were characterized using an enzyme-linked immunosorbent assay (ELISA) system under conditions that, only the antibodies with carbohydrate specificity were reactive with the solid-phase adsorbed (GlcNAc)n-BSA antigens. Inhibition assays using the (GlcNAc)n-BSA, (GlcNAc)n oligosaccharides, and the reduced oligosaccharides showed a relative specificity of the antisera for the chain length of the (GlcNAc)n sequences. For example, the anti-(GlcNAc)5-and anti-(GlcNAc)4-sera were inhibited best by the longer chain (GlcNAc)n ologosaccharides with the antibody combining sites directed mainly to the cyclic GlcNAc residues of the (GlcNAc)n-BSA conjugates. The antibody combining sites were in part directed to the acyclic moiety of the reducing end of the oligosaccharides as shown by the increased inhibitory activities of the reduced (GlcNAc)n oligosaccharides particularly, with the anti-(GlcNAc)2-and anti-(GlcNAc)3-sera. The best hapten inhibitors for the anti-(GlcNAc)2-BSA and anti-(GlcNAc)1-BSA sera were theN-butylamine derivatives of (GlcNAc)2 and (GlcNAc)1, respectively, indicating that the antibodies were also reactive with the secondary amine formed between the reducing end of the oligosaccharides and the e-amino groups of lysine.