A continuous membrane bioreactor (CMB) with Ceraflo ceramic microfilter was evaluated for the production of phenylacetylcarbinol (PAC) using 12-15 g dm(-3) Candida utilis. Compared with the classical continuous fermentation, the CMB process was shown to have higher biomass concentration (from 40% to 400% increase) and greater growth rate (from 3- to 9-fold) at dilution rates varying from 0 . 03 h(-1) to 0 . 23 h(-1). These advantages were partially offset by the reduced permeate flux caused by the increased biomass. Furthermore, an addition of only 3 . 0 cm(3) h(-1) benzaldehyde for 17 h (a typical bioconversion protocol) was found to kill the yeast, resulting in 27% dead organisms and 35% lysed organisms and their associated species. This led to a 100% flux decline during the course of PAC production over the above period.