Using as plasma source a wall stabilized argon arc working within a restrictedparameter range (inner tube diameter = 7 mm, pressure = 30-120 Torr, current = 5-20 A)) the existence of a BOLTZMANN equilibrium between spectral energy levels is checked by comparing measured occupation number densities of higher excited levels (N,,,, exp) with the corresponding number densitieg calculated under the assnmption of BOLTZMANN equilibrium (Nm, The methods for determination of the quantities N,,,,,,p, T, (2300-5405°K), T, (7170-9950°K) and N , (0.33 -2.4 x 1015 cm-3) needed for this comparison are described. It can be shown within the limit of experimental error that a BOLTZMANN equilibrium exists a t least for electron densities of N , > 3 10l4 ~m -~. The problem of energy balance of that type of arcs used in these experiments is discussed.