Coupling with two double mediator systems, menadione/ferricyanide and 2,6-dichlorophenolindoph-enol/ferricyanide, electrochemical method was employed to evaluate the cytotoxic effects of furfural on yeast cells. The yeasts under research include the glucose-fermenting yeast Saccharomyces cerevisiae and two xylose-fermenting yeasts Pachysolen tannophilus and Pichia stipitis. Measurements were made with microelectrode voltammetric method to assay the ferrocyanide accumulations arising from menadione or 2,6-dichlorophenolindophenol mediated reduction of ferricyanide by yeasts. The results obtained from 3 h incubation of cells suspensions by the presence or absence of increasing concentrations of furfural or furfural alcohol suggested that furfural and furfural alcohol actually impose inhibitory effects on three yeasts, and furfural alcohol was less cytotoxic than furfural. The xylose-fermenting yeasts under research were more sensitive to furfural than that of S. cerevisiae. For the first time, we showed that the joint utilization of menadione/ferricyanide and DCPIP/ferricyanide mediator systems in electrochemical measurements provides us with a potent and convenient tool for cytotoxic evaluation. (c) 2005 Elsevier Inc. All rights reserved.