Additon of pyruvate or leucine was found to be efficient for increasing the intracellular ratios of NADH/NAD and NADPH/NADP while reducing the coenzyme A concentration during the cultivation of Alcaligenes eutrophus. Poly-beta-hydroxybutyrate (PHB) accumulation was enhanced more than 2-fold since metabolic flux of acetyl-CoA into PHB synthetic pathway could be facilitated by the changes of the cofactor concentrations.