A method for systematically analyzing biochemical reactions in a cell was proposed. One of the characteristic features of biochemical reactions in a cell is that many components are participating and that quite many reactions are taking place. Also bio-separation processes are observed. We applied material-utilization diagrams to systematically grasp such a biochemical process. We used two diagrams. In the first diagram, the change in concentration for each component was presented, whereas in the second diagram, the deviation of each biochemical reaction from the equilibrium condition was displayed. Those diagrams suggested the possibility to improve the biochemical process, since they revealed the exergy losses caused by changes in concentration or biochemical reactions. (C) 2004 Published by Elsevier Ltd.