Clostridium thermocellum 27405 is a fermentative thermophile producing hydrogen and ethanol, along with CO2, acetate, formate and lactate from cellulosic biomass. Based on its genomic sequence, pyruvate serves as a common intermediate for end-product formation. The genome sequence also predicts specific genes whose expression may be required. We can verify how the various branches of pyruvate metabolism might be regulated by following changes in growth, end product synthesis, activities of enzymes involved in pyruvate metabolism, and corresponding mRNA levels (using quantitative PCR) of corresponding putative genes under different growth conditions. This is illustrated by describing the effects of additions of higher concentrations of single end products to the medium at the beginning of growth in batch cultures with 1.1g/l cellobiose as growth substrate. Such additions had little effect on growth. However, changes in concentrations of other end products were observed: H2 and acetate production increased with ethanol or lactate addition, formate increased with H2 addition, and ethanol increased with acetate addition. Pyruvate:fd oxidoreductase, hydrogenase (MV, NAD+, and NADP+ dependant), lactate dehydrogenase, alcohol dehydrogenase (NADH and NADPH dependant), and aldehyde dehydrogenase activities were observed in extracts of exponentially growing cells. Addition of individual end products did not affect the levels of enzymes activities assayed, except for hydrogenase, which increased in cells grown with added of H2 or lactate. Levels of mRNA for alcohol dehydrogenase adhE (gene 423), NiFe-hydrogenase (gene 3010), Fe-hydrogenase (gene 430) and pyruvate:ferredoxin oxidoreductase (gene 2796), determined by Q-PCR varied depending on the presence of specific added end products.