The metabolic response of lactose-assimilating yeasts to changes of cultivation conditions after addition of furfural into the medium was explored. Two yeast strains were studied-Candida blankii 35 with an oxidative metabolism, and C. pseudotropicalis 11 with a fermentative metabolism. Strains were cultivated in a chemostat under carbon limitation and dilution rates D=0.1 and 0.25 h(-1). During the transition period after a shock treatment with 0.04% furfural, changes of the following enzymes of the carbon metabolism were studied: hexokinase (HK), glucosephosphate isomerase (GPI) and glyceraldehyde-3P-dehydrogenase (GAPD) of the glycolysis, glucose-6P-dehydrogenase (GPD) from the pentosophosphate cycle, as well as beta-galactosidase. Results show that during cultivation of C. pseudotropicalis 11 at D=0.1 h(-1), furfural concentration of 0.04% caused increase of the glycolytic enzyme activities, while the level of GPD activity remained rather constant. At the higher dilution rate D = 0.25 h(-1) the effect of furfural brought to a significant decrease of all enzyme activities studied, except beta-galactosidase, for which activity registered at both dilution rates was significantly higher. During cultivation of C. blankii 35 at D=0.1 h(-1), furfural brought to lower activities of GPI and GPD, while HK activity was not affected by the inhibitor, and that of GAPD increased. The furfural shock at D=0.25 h(-1) leads to increased activity of the three glycolytic enzymes, while that of GPD was 33.6% lower as compared to control. Addition of furfural into the cultivation medium of the oxidative strain caused decrease of beta-galactosidase activity. (c) 2006 Elsevier Inc. All rights reserved.