X-ray spectroscopic methods have been increasingly used in recent years in studying dense hightemperature plasmas produced by sources relying on the vacuum spark, the plasma focus, laser-beam or electron-beam interactions, and exploding wires. The plasma produced in such sources is usually in a state that is intermediate between thermodynamic and coronal equilibrium so that the intensities in the spectra of multiply-charged ions are largely determined by the kinetics of excited-state relaxation. An analysis is given of the methods available for calculations of cross sections and rates of relaxation of excited states under electron and ion impact. The relative intensities of x-ray lines and their possible use in plasma-density diagnostics are examined. The effects of electric and magnetic fields in plasmas on line spectra of multiply-charged ions are briefly discussed.