Degradative and n.m.r.-spectroscopic studies have been carried out on a novel mannitol teichoic acid extracted from the cell wall of bacterium N.C.T.C. 9742, for which the name Brevibacterium iodinum has been proposed. The backbone of the polymer is a poly(D-mannitol phosphate) containing 1----6 phosphodiester linkages. In most residues, pyruvic acid is acetal-linked to positions 4 and 5 of the mannitol. About half of the mannitol residues carry a beta-D-glucopyranosyl substituent at position 2. The glucosylmannitol was isolated and thoroughly characterized. At least 24 products were detected by ion-exchange chromatography and paper electrophoresis after alkaline hydrolysis of the polymer. Not all of these products could be identified. The main mechanistic pathways for depolymerization by the cleavage of phosphodiester linkages during alkaline hydrolysis involved (a) participation by the 2-hydroxy group and a cyclic phosphodiester intermediate (leading to a series of mannitol-based products) and (b) participation by the 3-hydroxy group in the cyclization of mannitol (leading to a series of products based on 1,4-anhydromannitol). The presence of glycerol phosphates in hydrolysates could be ascribed either to a linkage unit or to a separate glycerol teichoic acid. The mannitol teichoic acid was absent from the cell walls of Brevibacterium linens and Brevibacterium epidermis (one strain of each was examined).