The title compounds were degraded in 0.099M oxygen-free aqueous NaOH at 25°, and sometimes 45°. Cellobiose degraded primarily to 3-deoxy-2-C-hydroxymethyl-D-pentonic (“isosaccharinic”) acids, plus the series of 3- to 6-carbon 3-deoxyaldonic acids and glyceric acid also produced from glucose. No disaccharide acids Indicative of a “stopping” reaction were formed. However, formation of 3,4-dideoxy-5-hexulosonic acid from cellobiose indicates that elimination of OH-3, necessary for the “stopping” reaction, did occur, but that the glucosyloxy substituent at C-4 was also eliminated in the same reaction sequence. The major products from 3, 6-anhydro-4-0-methyl-D-glucose and 3,6-anhydro-4-0-(β-D-gluco-pyranosyl)-D-glucose (3,6-anhydrocellobiose), 3-deoxy-D-hexonic acids and 3-deoxy-2-C-hydroxymethylpentonic acids, respectively, also indicate primary reaction sequences involving multiple substituent elimination. However, in contrast to cellobiose, 3,6-anhydrocellobiose also yielded a disaccharide product indicative of a “stopping” reaction. Mechanisms are proposed to account for the primary products of each substrate.