The Gissar-Kokshal fault zone south of the Tien Shan Mountains in central Asia is one of the most active areas of intraplate seismicity in the world. Since 1949 four earthquakes greater than magnitude 6.5 have occurred along the section of this fault north of the Pamir Mountains, almost completely filling a seismic gap which had existed for at least 80 years. The two most recent of these earthquakes, the 1974 Markansu (Ms=7.4) and 1978 Zaalai (Ms=6.7) events, were each preceded by a short period of increased activity in the future epicentral area some years prior to the main shock. The largest earthquake within this active period occurred at the same location as the future large shock. A segment adjacent to the 1978 earthquake, occupying the only unbroken portion of the former gap, has recently shown a similar burst of activity, suggesting that it may be the site of the next large earthquake of this sequence. Large premonitory earthquakes are also observed near the sites of seven other earthquakes with magnitudes 7.0 to 8.3 in the Tien Shan since 1880. In all of the cases studied, the premonitory time interval and magnitude of the premonitory earthquake increase with the size of the main shock.