The occurrence of iduronic acid in the cell surface glycoprotein of halobacteria is described. This hexuronic
acid is not only found in protein-linked oligosaccharides in halobacteria but does also exist in the corresponding
dolichol-linked precursors. These findings were unexpected, as iduronic acid is a typical constituent
of animal ~ycosamino~ycans, and its biosynthesis is so far known to occur by epimerization of a glucuranic
acid residue within the completed carbohydrate chain finked to protein.