The article discusses models for the metabolic production of oxalate from xylitol in humans. It has been proposed previously that oxalate precursors may be formed in the transketolase reaction during the metabolism of xylitol. In Australia, in 1969, patients receiving parenterally administered xylitol were observed to suffer a syndrome of adverse reactions which included calcium oxalate deposition in the brain and kidneys. Glycolaldehyde is a known oxalate precursor and the transfer reaction catalysed by transketolase proceeds by a bound, two-carbon intermediate referred to as an "active glycolaldehyde." Since xylitol can be metabolised to D-xylulose 5-phosphate by D-xylulose reductase and xylulokinase, it has been proposed that, in unusual circumstances such as an excess of D-xylulose 5-phosphate, the active glycolaldehyde transketolase intermediate may fail to transfer the glycolaldehyde to an acceptor molecule and, instead, release free glycolaldehyde.