The interdisciplinary research project MODEXA aims at developing model-based methods and tools for the optimal design of experiments on living cells with the goal of quantitative elucidation of structure and dynamics of signal transduction cascades. Stimulus-experiments on cells, development of network models for the signal transduction networks under investigation and the model-based planning of experiments are linked in an iterative workflow, enabeling the identification and parameterization of adequate network models. Experimental data structures, the generation of model alternatives, model discrimination and parameter identification are intended for implementation into a modular software tool using established interfaces.