The pulsed electroacoustic (PEA) method has been used to measure space charge phenomena in polymers. We have developed a new transient PEA system, and observed space charge profiles of low-density polyethylene (LDPE) films at 1 ms intervals during breakdown teats at various temperatures. In order to clarify the relationship between the space charge and external circuit current at intrinsic electrical breakdown of polymer insulating films, we have developed an external circuit current measuring unit for the transient PEA system. This paper shows space charge dynamics and external current observed during a short time breakdown test of a 100 /spl mu/m thick LDPE film at 90 /spl deg/C. The experiments revealed that positive charge injection is one of the most important factors affecting the intrinsic breakdown of LDPE in the high temperature region.