Auroral radar measurements performed with the EISCAT facility are presented. Backscatter cross sections of the irregularities produced by the two-stream (Farley-Buneman) or grdient drift plasma instabilities have been recorded with a range separation of 1.5 km, corresponding to a spacing of successive values in height of about 0.4 km. The apparent height profiles of the backscatter have a width of about 5--6 km and occur between 95 and 112 km altitude,with a mean at 104 km. Very often, fast motions of the backscatter layers are observed which can be explained as fast moving ionospheric structures controlled by magnetospheric convection. The maximal time resolution of the measurements is 12.5 ms. The statistics of the backscatter amplitudes at this time resolution is close to a Rice distribution with a Rice parameter a≈3.7. The observed backscatter spectra do not change significantly in shape when the integration time is reduced from 5 s to 100 ms. ¿American Geophysical Union 1990