In a pulsed discharge, the temporal and radial behavior of the population densities of He(2 1S), He(2 3S), Hg(6 3P2), and Hg(6 3P0) is studied experimentally, and the time variation of the intensity of sidelight of Hg II at the 567.7‐ and 6 15.0‐nm lines is also measured with changing He partial pressure. The temporal and radial behavior of the laser action of a Hg ion laser is explained in terms of the temporal and radial behavior of the reactants in the Penning‐like excitation process, and furthermore, it is found that the populations of these reactants are dependent upon the distribution of the electron temperature.