We describe a new two-frequency lidar for measuring Na temperature profiles that uses a stabilized cw single-mode dye laser oscillator (rms frequency jitter <1 MHz) followed by a pulsed-dye power amplifier (140 MHz FWHM linewidth) which is pumped by an injection-locked Nd:YAG laser. The laser oscillator is tuned to the two operating frequencies by observing the Doppler-free structure of the Na D2 fluorescence spectrum in a vapor cell. The lidar technique and our initial observations of the temperature profile between 82 and 102 km at Ft. Collins, CO (40.6¿N, 105¿W) are described. Absolute temperature accuracies at the Na layer peak of better than ¿3 K with a vertical resolution of 1 km and an integration period of approximately 5 min were achieved. ¿ American Geophysical Union 1990