Rhizobium meliloti associates symbiotically with alfalfa by forming root nodules in which the bacteria reduce atmospheric N2 into products useful to both organisms. Nod factors are signal molecules, lipooligosaccharides, produced by the bacteria that trigger nodule formation in the plant host. Nod Rm-1 consists of a beta-1,4-N-acetyl glucosamine tetrasaccharide from which the N-acetyl group at the non reducing end is replaced by a fatty acid and the N-acetyl glucosamine at the reducing end is sulfated at position 6. By in vitro incubation of electroporated cells in the presence of [35S]PAPS or UDP-[14C]GlcNAc a labelled compound has been obtained with the properties of the in vivo produced Nod Rm-1 factor, as judged by HPLC, TLC and HPTLC techniques. The [14C]GlcNAc labelled compound has also hair root deformation activity on alfalfa plantlets indicating that a functional Nod Rm-1 factor has been synthesized in vitro.