Abstract: It has become well known that simulation can be used to investigate complex biomedical systems in situations where traditional methodologies are difficult or too costly to employ. Once the model, constructed to represent important aspects of the system under evaluation, has been validated, it may be used to investigate the effects of differences in the system inputs, changes in initial conditions, or its environment, and alterations in the system structure. Many recent advances in technology, such as the Next Generation Internet, high bandwidth communication, object oriented software, distributed and parallel processing, and visualizing techniques, have greatly enhanced the power and expressiveness of simulation. We give two examples where Monte Carlo cellular automaton simulation is applied to study cancer growth and Min protein dynamics.