A biological fuel cell was constructed in which the metabolism of glucose by yeast provided the electrons. A two compartment plexiglass fuel cell was constructed with platinum electrodes separated by a proton conducting membrane. One half of the cell contained yeast, Saccharomyces cerevisiae, glucose, and an electron mediator, methylene blue. The other half contained an electron acceptor, potassium ferricyanide. Electrons produced during the metabolism of glucose by the yeast were captured by the methylene blue and transferred to the platinum electrode, traveled through the external circuit to the cathode compartment, and were finally accepted by the potassium ferricyanide. When yeast was added to the fuel cell the open circuit potential was similar to 0.5 V. Electrical current was measured while holding the cell voltage at 0.3 and 0.1 V. Current output was optimized for the initial concentration of yeast, temperature, glucose concentration, agitation and oxygen content. The optimum conditions for producing current within the scope of this study were obtained with agitated, partially oxygenated electrolyte at 45 degrees C containing 0.1 M glucose. (c) 2006 Elsevier B.V. All rights reserved.