Two alpha-mannosidase enzymes (EC 3.2.1.24) and an alpha-1,2-mannosidase enzyme (EC 3.2.1.113) were compared for their ability to synthesise hetero-oligosaccharides by the equilibrium approach (condensation reaction). A panel of disaccharide accepters was used and product yields and product spectra determined. Choice of enzyme had a significant influence on product yield, with yield being dependent on enzyme and substrate combination. Most of the enzyme/substrate combinations tested gave 1 --> 6 linked manno-oligosaccharides as the principal product. Mannose was linked to lactose, cellobiose and lactulose by both 1 --> 3 and 1 -->,6 linkages in ratios that depended upon the enzyme used. Homo-oligosaccharide (mannotriose) formation was found in all but one of the enzyme/substrate combinations tested and, in the case of the alpha 1,2-mannosidase, the structure of the mannotrioses depended upon the acceptor used. Formation of hetero-oligosaccharides over homo-oligosaccharides could be favoured by use of low mannose : acceptor ratios.