The synthesis of sufficient amounts of oligosaccharides is the bottleneck for the study of their biological function and their possible use as drug. As an alternative for chemical synthesis, we propose to use Escherichia coli as a "living factory." We have addressed the production of the Galpalpha(1-3)Galpbeta(1-4)GlcNAc epitope, the major porcine antigen responsible for xenograft rejection. An E. coli strain was generated which simultaneously expresses NodC (to provide the chitin-pentaose acceptor), beta(1-4) galactosyltransferase LgtB, and bovine alpha(1-3) galactosyltransferase GstA. This strain produced 0.68 g/L of the heptasaccharide Galpalpha(1-3)Galpbeta(1-4)(GlcNAc)(5), which harbours the xenoantigen at its non-reducing end, establishing the feasibility of this approach. (C) 2003 Elsevier Science (USA). All rights reserved.