Cell Growth Simulation (CGS) is a software package that simulates the growth of cell cultures, and the effects of different types of agents on the cell populationsin vitro. It is a stochastic simulation system based on the cell cycle kinetics. Experiments involving DNA synthesis blocking, mitosis inhibition, labelling and cell kill can be simulated by imitating agents such as thymidine, aphidicoline, hydroxyurea, vincristine, vinblistine, colcemid and others. The model to be simulated is described by the user according to his theoretical convictions, The system provides numerous facilities to help the user describe an experiment and examine the simulation results. A menu driven interactive scheme is used to communicate with the user. CGS has a modular structure and its general structure, design philosophy and capabilities are presented. The system has been developed through the cooperation of industrial engineering, cell biology, medical oncology and computer programming disciplines. It is implemented on PCs with hard disks and 512K bytes of RAM using the True Basic language.