We develop a method for the rapid determination of the moment tensor of large worldwide earthquakes, by inversion of long-period data recorded by the MEDNET regional network, and we apply it to the most significant events of 1990: March 3 (Fiji) and 25 (Costa Rica), May 12 (Sakhalin), 20 (Sudan) and 30 (Romania), June 20 (Iran), July 16 (Luzon) and December 30 (New Britain). The comparison with CMTs and moment tensors by USGS shows that an advanced regional seismic network is capable of providing reliable and rapid control of the seismic source for worldwide seismicity. ¿ American Geophysical Union 1992