A two‐wavelength He:Ne laser heterodyne system has been successfully used to measure electron number densities in the range from 4 × 1012cm−3to 1011cm−3, over a path length of 24 cm. These experiments were performed on a single‐shot basis in pulsed argon discharges. The spatially resolved laser measurements compared quite favorably with integrated electron density measurements made with a microwave cavity operating in theTM010mode.