A pulsed probe has been used to measure certain parameters of a time varying plasma in mercury vapor. Langmuir probe characteristics have been obtained by pulsing the probe voltage to successively higher values for &mgr;sec intervals at specific times relative to a repetitive discharge pulse. Curves showing the time dependence of the plasma potential, electron temperature, and electron density relative to this pulse are presented. The probe characteristics do not exhibit a sharp break at the plasma potential. This is related to a disturbance of the plasma by the probe. A novel and precise technique for determining the actual plasma potential is described. This technique depends upon the abrupt appearance of a spike on the leading edge of the probe current pulse.