The verification of transversal electromagnetic (TEM) waveguides, especially GTEM cells, is described in the standard IEC 61000-4-20 in the frequency and time domain. The verification in time domain is based on a nuclear electromagnetic pulse (NEMP) with a double exponential waveform, with is defined by two parameters, the rise time and pulsewidth, and the given parameter limits. A verification of the transmission qualitiy of a GTEM cell for arbitrary transient signals based on these parameters is not possible. Furthermore, it is not possible to identify critical frequencies of the performed waveguide with such an ultra-wideband pulse. Due to new upcoming signal shapes in the communications engineering and the use of transient signals in electromagnetic compatibility (EMC) issues, a verification of waveguides for these waveform is essential. The method presented in this paper allows the qualification of a TEM waveguide for arbitrary transient signals. A signal comparison based on a correlation is performed, which quantifies the transmission quality of a waveguide for the performed transient shape. © 2017 Walter de Gruyter Berlin/Boston.