The Arecibo 430-MHz radar was used in October and November of 1974 to make preliminary measurements of collision-dominated Thomson scatter spectra in the 80- to 100-km altitude region. A technique for interpreting the altitude variations of the collision-dominated spectra is presented. This technique employs the relaxable assumptions of an isothermal atmosphere and ion-neutral collision frequency variation with altitude according to the Barometric Law. Within these assumptions, temperature, collision frequencies, and total neutral number densities are inferred. We found the winter tropical mesopause region to be slightly warmer and denser than is indicated in the Cira (1972) standard atmosphere.