A new solid phase method for the synthesis of complex oligosaccharides is described. The method involves attachment to phenolic polystyrene of the first carbohydrate unit, through its anomeric position and via a photolabile linker, using dimethylthiomethylsulfonium triflate as an activator. Reiteration of the glycosidation process allows stereocontrolled growth of linear or branched oligosaccharides in high yield. Cleavage from the resin is efficiently achieved photolytically. The application of the method to the total prepn. of the heptasaccharide phytoalexin elicitor (HPE) is described.