The electron density and the electron temperature in a low-pressure argon mercury positive column are determined using Thomson scattering. Special attention has been given to the stray light reduction in the Thomson scattering setup. The results are obtained in a discharge tube with a 26 mm diam, 5 mbar of argon, a mercury pressure in between 0.14 and 1.7 Pa, and an electric current ranging from 200 to 400 mA. The systematic error in the electron density is 15%, the statistical error is 25%. The total error in the electron temperature is 10%–20%. © 2000 American Institute of Physics.