A method is described for determining the radial density distribution of the ground and the first excited states as well as the electron temperature distribution in multielement plasmas containing mercury. It is based on the spectroscopic measurement of the plasma emissivity at the maximum of self-reversed lines and the population density of a high-lying excited state. The method is independent of equilibrium assumptions and can be used in diagnostics of nonequilibrium plasmas. The proposed method was verified for the plasma of a 5 bar discharge in mercury. Plasma underionization and nonequilibrium excitation are observed spectroscopically in the bulk of the discharge. The experimental data are interpreted in terms of nonequilibrium effects. Comparison of the results obtained initially, and then assuming local thermodynamic equilibrium ͑LTE͒, shows clearly considerable departure of the plasma from LTE.