A key element in successful seismic verification of a nuclear test ban treaty is the capability of a sparse network of seismic stations to accurately locate regional events. We have investigated the regional location accuracy of the Regional Seismic Test Network (RSTN), a five-element, three-component network in eastern North America, using 62 events varying in size from magnitude 3.0 to 5.1. Applying an algorithm which allows inclusion of back-azimuth estimates as well as travel times, we determined a median location error of 23 km for the data set relative to the PDE locations. Considering the large station spacing (1500 km) and a few data used in the locations (2 to 4 stations), the RSTN location accuracy is remarkably good; the results imply that a widely spaced network of single, three-component stations could reliably locate regional seismic events. ¿ American Geophysical Union 1989