The stoichiometry of maintenance and carbohydrate storage as well as ajmalicine production kinetics of non-dividing Catharanthus roseus cells in the second stage of a two-stage batch process were investigated. For-the mathematical description of these processes, a simple structured model with 5 parameters is proposed. In the model the biomass is divided In two compartments: active: biomass and storage carbohydrates. In induction medium (standard medium without phosphate, nitrogen-and hormones), biomass formation, glucose consumption, and CO2 production appeared to be constant:in time. Therefore, it is assumed that the active biomass level is constant. The maintenance coefficient m(S), and the yield of storage carbohydrates on glucose Y-SC were optimized by fitting the model on experimental data: 0.003 C-mol/C-mol/h and 0.82 C-mol/C-mol, respectively. Production kinetics were incorporated in this model and related to the active biomass fraction. The maximum specific ajmalicine production rate q(p)(max) was fitted On the data: 7.5 mu mol/C-mol/h. The model was tested at several different experimental conditions, and proved to describe the experimental results adequately. An independent experiment at a very high cell density in order to obtain maximum product formation was used to validate the model. It provided a satisfactory description of the results, but the final ajmalicine concentration (198 mu mol/L after 18 days) was lower than the calculated maximum, due to accumulation of inhibiting gaseous metabolites.