The production of carbon dioxide from transketolase-catalysed condensations has been studied. The effects of carbamate formation, carbon dioxide dissociation and gas/liquid interfacial area were evaluated as potential causes of activity loss on account of by-product carbon dioxide production. At low pH values physical effects (gas/liquid interfacial area) were dominant, while at higher pH values carbamate effects dominated. However. neither of these effects were found to lead to a significant additional activity loss under the conditions chosen. Residual activity loss was evaluated at intermediate pH values and attributable to non-specific protein oxidation, indicating the need to operate the process under reducing conditions.