An algorithm for obtaining temperatures and volume emission rate profiles in the mesosphere and lower thermosphere from HRDI measurements is described. Temperature and volume emission rates are derived via perturbation theory by comparing measured brightness to brightness computed from the forward model described here. Error analysis shows that the method recovers the temperatures with an error of 7 ¿K and volume emission rates with an error of 3% from 80 to 100 km, providing global measurements of these fields in this altitude range for the first time. Results show the structure of the cold summer mesopause near the poles, the semiannual oscillation, and the diurnal tidal oscillations at the equator. ¿ 1998 American Geophysical Union