Sucrose, the ubiquitous constituent of higher plant tissues, is frequently accompanied by higher molecular weight oligosaccharides containing Dgalactose residues. The commonest of these are raffinose (a-D-galp-(l -* 6)-a-D-Gp-(1 -* 2)-8-D -Fruj) and higher homologues which occur in relatively high concentrations in many dormant seeds and other plant organs (3, 6). Raffinose and stachyose (ae-D-Galp(I ---6) -c)-D-Galp(l 1 * 6) -a-D-G(I 1 > 2)-,f-D-Frnf) have also been detected in sieve-tube exudates from several species and, therefore, presumably form part of the organic material which is translocated (10). The biosynthesis of the raffinose family of oligosaccharides occurs during seed maturation and in vitro it has been demonstrated that raffinose is formed when sucrose,a-n-,galactose 1-phosph4te and UTP3 are incubated with an enzyme preparation from dormant broad bean (Vicia faba) seeds (1). This paper describes further studies which implicate UDP-D-galactose as the galactose donor in this system.