Oxidation of tissue sections by 25-30% (v/v) acetic anhydride (AA) in dimethyl sulfoxide (DMSO) resulted in facile induction of tissue carbonyls readily localized with Schiff's reagent and o-dianisidine but not with the 3-hydroxy-2-naphthoic acid hydrazide-tetraazotized diorthoanisidine method. Carbonyls generated by AA-DMSO oxidation were confined predomintly to substrates containing pyranosides. Oxidized furanosides, as represented by deoxyribonucleic acid and ribonucleic acid, gave only a residual color reaction. The AA-DMSO method possesses an advantage in that the oxidation of tissue polysaccharides does not proceed beyond the formation of carbonyly and is particularly suited for use after formol fixation.