A modified diffusion approximation was constructed for assessing the collisional-radiation kinetics in a nonequilibrium cesium plasma. Calculations were performed for the contribution to the ionization from associative ionization on pair collisions between excited atoms. At low electron concentrations less than or equal to 10¹³/cm³, and electron temperatures less than or equal to 2500 K, and at elevated atomic temperatures greater than or equal to 800-1000 K, associative ionization involving two excited atoms made a substantial contribution to the ionization. On the other hand there was usually no appreciable contribution to the ionization from associative ionization on collision between an excited and a normal atom.