In seeking to gain a better understanding of the pyrolysis of polysaccharides, the pyrolytic behavior of a variety of naturally occurring and synthetic polysaccharides has been studied. Among the former were various glucans containing different linkage types, and for the latter, synthetic polymers were produced by thermal polymerization of a glucoside and of a xyloside. The study has focused on the effects which linkage types and inorganic additives have on pyrolytic pathways, with emphasis on the chemical mechanisms involved in the formation of one-, two-and three-carbon products, specifically glycolaldehyde, acetol, acetic acid, and formic acid. These compounds are the major non-aqueous components of the -60" condensate of the vacuum pyrolysate after removal of tar by room temperature condensation. ' %Y labels in synthetic glucans were used to reveal the origins of these compounds. In general, the results show that each compound is formed by more than one mechanism. Specifically, glycolaldehyde derives mostly from C-l and C-2 of the glucose monomers, with C-5 and C-6 also contributing significantly. Acetol and acetic acid derive mostly from contiguous carbons that include a terminal carbon (C-l or C-6), most often C-6, appearing as the methyl carbon. About half of the formic acid arises from C-l. Some mechanisms derived from solution chemistry are proposed.