The accurate characterization of biomass is critical for development of bioenergy feedstocks and their utilization. Most analytical approaches involve acid hydrolysis of the polysaccharides in biomass, leaving most of the lignin as insoluble residue. A limitation of this approach is that the same conditions used to hydrolyze polysaccharides also degrade the liberated monosaccharides. The NREL-compiled procedures account for this effect with "Sugar Recovery Standards", in which a solution of the expected monosaccharides is prepared and subjected to the dilute-hydrolysis portion of the procedure; however, this tends to overestimate monosaccharide degradation and introduce bias between polysaccharides of different lability. The following recommended method modifications are intended to reduce these errors: (1) quantification of immediate degradation products of monosaccharides and their stoichiometric addition to the monosaccharide yield; (2) the adjustment of this combined yield with sugar recovery standards; and (3) preautoclave analysis of hydrolyzates to improve the estimation of monosaccharide concentration profiles for adjustment calculations.