Thomson scattering diagnostics of a free burning argon arc are reported. The electronic plasma parameters are measured with the aid of a periodically pulsed Nd:YAG laser with second harmonic generation. With arc currents in the 100 A range, the electron temperature and density on the axis are Te approximately=1.7 eV and ne approximately=5*1016 cm-3, respectively; and the scattering parameter alpha is close to 1.5. The ion feature is resolved with the aid of a narrow-bandwidth dye laser tuned relative to a spectrally fixed detection channel. Electron and ion temperatures are in satisfactory agreement.