In this report we summarize the results of 22 months of observations of Arctic mesosphere echoes with the 50-MHz radar at Poker Flat, Alaska. Operation with a partially complete system began in February 1979 and has continued on a nearly continuous basis to the present time. The altitude range of the mesospheric echoes obtained during this period shows a pronounced seasonal variation. During summer months the mesospheric echoes are relatively continuous in time and extend from about 80 to 100 km with an unexpectedly strong peak in signal-to-noise ratio at about 85 km. In contrast, in nonsummer months, mesospheric echoes are less intense and occur at lower altitudes in the range from 55 to 80 km. These lower-altitude nonsummer echoes are observed primarily during daytime hours when energetic auroral particle precipitation (as determined by the Poker Flat 30-MHz riometer) is present.