In Candida albicans, cyanide and antimycin A inhibited K+ transport, not only with ethanol-O2 as the substrate, but also with glucose. The reason for this was that they inhibited not only respiration, but also fermentation, decreasing ATP production. Measurements of oxygen levels in cell suspensions allowed identification of the electron pathways involved. NADH fluorescence levels increased in the presence of the inhibitors, indirectly indicating lower levels of NAD+ and so pointing to glyceraldehyde-3-phosphate dehydrogenase as the limiting step responsible for the inhibition of glycolysis, which was confirmed by the levels of glycolytic intermediaries. The cyanide effect could be reversed by hydrogen peroxide, mainly due to an activity by which H2O2 can be reduced by electrons flowing from NADH through a pathway that can be inhibited by antimycin A, and appears to be a cytochrome c peroxidase. Therefore, the inhibition of glycolysis by the respiratory inhibitors seems to be due to the decreased availability of NAD+, resulting in a decreased activity of glyceraldehyde-3-phosphate dehydrogenase. Compartmentalization of pyridine nucleotides in favor of the mitochondria can contribute to explaining the low fermentation capacity of C. albicans. Similar results were obtained with three C. albicans strains, Candida dubliniensis and, to a lower degree, Candida parapsilosis.