It has been proposed previously that oxalate precursors may be formed in the transketolase reaction during the metabolism of xylitol. It is shown in this paper that fructokinase and aldolase, purified from human liver, provide an alternative model in that, in coupled sequence, they produce glycolaldehyde, an oxalate precursor, from D-xylulose via D-xylulose 1-phosphate; D-fructose does not give rise to glycolaldehyde. It is concluded that metabolic pathways based on a combination of the transketolase, fructokinase and aldolase reactions can account for the production of glucose, lactate, tetronates (C-threonic and D-erythronic acids) and oxalate (precursors) during the metabolism of xylitol administered parenterally.