During the summer of 1995, two MF radars located at Hawaii and Puerto Rico were in operation to measure mesospheric motions. We use the data obtained at the two sites to study the longitudinal variability of mean winds, planetary waves, and tides. On average the winds at Puerto Rico were more westward and equatorward than those at Hawaii. Quasi 2-day planetary wave activity was evident most of the time from June 28 to July 25. The quasi 2-day wave had a zonal wave number (m) of 3 during one occasion and 4 during another, and the periods of the two planetary waves were 56 and 48 hours, respectively. The diurnal tide at Puerto Rico was stronger than that at Hawaii above 86 km, and the semidiurnal tide at Hawaii was strongly damped in the altitude range of 90--98 km. Both the semidiurnal and the diurnal tides were apparently modulated by longer-period waves, which was perhaps the most important factor in accounting for their large spatial and temporal variability. The phase difference at the two sites deviates considerably from the expectation of purely migrating tides. ¿ 2000 American Geophysical Union