The mitogen activated protein kinase (MAPK) cascade is one of the most prominent and well-studied signaling networks. The pathway has control over such diverse cellular functions as cell proliferation, migration, and differentiation. In addn. to its well-demonstrated importance for regulating cellular function, its structure or design is also of interest to scientists and engineers seeking to understand the cause of systemic failures of signaling and for the design of cellular circuits. From the circuit perspective, the most important property of a MAPK cascade is its ability to display "zero-order ultrasensitivity" or a sharp switch-like response without cooperative, Hill-type enzymes. In this presentation, we will discuss the results of our computational studies on how the properties and the interactions of individual modules of a MAPK network det. the characteristics of the network response. [on SciFinder (R)]