Monosaccharides and polysaccharides are chemically modified when they are subjected to rf plasmas derived from oxygen, nitrogen, or argon. The plasma treatment converts hydroxyl groups within the bulk to carbonyl groups on the order of one per anhydroglucose unit. On the surface, the concentration of carbonyl groups is greater than in the bulk. The activated surfaces formed by the plasma treatments are stable for at least 1.5 h. The observed spectral (IR, ESCA, and ESR) changes of the irradiated samples are the direct result of the plasma and not the secondary result of plasma-activated surfaces reacting with the atmosphere.