Incoherent scatter measurements of temperature in the lower thermosphere (100–125 km) at Millstone Hill (42°N) and St. Santin (45°N) are analyzed to determine the influence of thermal tides propagating from the lower atmosphere. The average temperatures from several years of measurements exhibit a 12-hour oscillation having a downward phase progression with height. The characteristics of this oscillation are found to be in excellent agreement at the two mid-latitude stations. The average amplitude reaches a maximum of 11% of the mean at a height of 116 km and a local time of 6.6 hours, the vertical wavelength increasing from 40 km at 105 km to 64 km at 120 km. From a comparison with theoretical predictions we conclude that this oscillation is predominantly the solar (2, 4) tidal mode; however, the rate of damping above 116 km is larger than that given by dissipative theory. The results also reveal a significant variability in the amplitude and phase of the tidal oscillation from one observing period to the other. Seasonal temperature averages indicate a smaller amplitude in winter than in summer or at equinoxes because of a larger phase variability in winter. An empirical model of the mid-latitude temperature structure in the lower thermosphere based on the radar measurements is also presented.