It is quite important to consider the "cellular metabolism as a network or system", and the participating reactions in their "entirety", rather than on an individual basis. From this viewpoint, we are trying to integrate the informations from gene and protein expressions to metabolic pathway regulations. In particular, we are focusing on the research on the metabolic flux analysis based on ¹³C labeling experiments and the measurement of intracellular isotope distributions using NMR and/or GC-MS etc. Our final goal is to develop the quantitative model for the cell.