A system, and associated article of manufacture, in which biochemical reactions of the system are modeled by using spatially heterogeneous stochastic Petri-net modeling. The biochemical reactions of the system to be modeled are defined. A spatial decomposition of the system is defined by defining regions of a space in which the system is to be modeled and by assigning each biochemical reaction to a region, such that the system is spatially heterogeneous. Relationships for inter-region movement of reactants of the biochemical reactions are defined as flux, advection, convection, and/or diffusion-based molecular movements. The system of the biochemical reactions is then modeled by modeling the biochemical reactions of each region as a spatially homogenous stochastic Petri-net and by modeling the inter-region movement of the reactants based on the relationships as defined.