alpha-D-Mannnose occupies the terminal position on the N-linked carbohydrate side chain of BDV-specific gp17 (Stoyloff at al., 1994). A hydrophobic derivative of this sugar residue, the 1-O-benzyl-6-O-trityl-alpha-D-mannnopyranoside (1BGTM), showed a potent and selective inhibition of BDV-replication in vitro, using a range of host-cell/virus systems. When tested in comparison with the unmodified sugar, 1B6TM inhibited the infection in a dose-dependent manner up to 100% without effecting cell viability. After removal of the compound, the antiviral effect remained for several hours. These results suggest that simple modified carbohydrate molecules of BDV-specific sugar residues are able to interfere with virus replication.