The environmentally benign and stereocontrolled glycosidations of mannopyranosyl sulfoxides and alcohols using a heterogeneous solid acid, Nafion-H or sulfated zirconia (SO4/ZrO2) as a new activator for the direct syntheses of both the alpha- and beta -mannopyranosides have been developed. (C) 2001 Elsevier Science Ltd. All rights reserved.