Deacetylation of the pentulose tetraacetate with barium hydroxide and preparative thin layer chromatography of the crude reaction product on microcrystalline cellulosez1 gave L-threo- pentulose (VII), characterized as the crystalline p-broniophenylhydra-L-threo-Pentulose showed a particular sensitivity to alkali as indicated by the formation, during the deacetylation process, of several products as detected by thin layer chromatography.