There is a necessity to include sensors, e.g. on the basis of resistors, in the design of organic electronic devices in order to extend the range of possible applications, mentioned in the last iNEMI roadmap (2009). It is essential to identity potential organic resistive materials, the processes and methods to structure them and to characterize their resistive properties on flexible substrates including their reliability. In this paper we focus on the resistive properties of conductive polymer screen printed in a roll-to-roll process on foil. One of the most important issues is their stability under different electrical and non electrical influences such as mechanical, thermal stress together with humidity. Highly isolating flexible substrates make the devices even more susceptible to transient electrical stress events like Electro Static Discharge (ESD). The ESD behavior of thick film resistors has been reported in several studies, using RC pulses, which lead to HBM-like discharges. In order to investigate the behavior at high current densities, a pulsed measurement technique was applied to polymer resistors on flexible substrates. The analytical test technique of Transmission Line Pulsers (TLP) allows, on the basis of square pulses, the in-situ monitoring of the voltages and currents at the Device Under Test (DUT) during pulsing and helps to gain fundamental insights into the electrical behavior at higher current densities. The transient electrical stress on the device exceeds its specified safe operation conditions. The influence of the pulse width and amplitude on the current-voltage behavior was investigated on polymer film resistors on flexible substrates and it is shown that parametric failure or catastrophic damage can occur.