The Arecibo 430 MHz incoherent scatter radar is used to measure the ion-neutral collision frequency and temperature of the atmosphere in the 70 to 100 km altitude range. Theses parameters are determined over altitude segments that are comparable to the scale height of the mesosphere. The spectra scattered from the mesosphere are collision dominated, that is, for the Arecibo radar frequency, &psgr;i>1 at all altitudes observed. Analysis of the widths of these spectra show that both the temperature and collision frequency values argree quite favorably with the Cira model atomosphere for the summer months.