Immunochemlcal studies of the seroloecally active 0-side cham of the Shgeila somel phase I hpopolysacchande have revealed a structure conslstmg of some carbohydrate components I-' that were hltherto unknown Recently, an ammo sugar has been Isolated2 wluch was tentatively characterized as a 2-ammo-2-deoxyhexuromc acid havmg a conflguratlon other than 911rc0, gala&o, or manno We now report the ldenttficatlon of ths sugar as 2-ammo-2-deoxy-L-altruromc aad, apparently hitherto unknown m Nature