JANUARY 1972 SEISMOLOGISTS FROM SEVERAL COUNTRIES MET IN Cambridge, Massachusetts, to discuss progress in seismic techniques for detecting and identifying underground nuclear explosions. At this meeting there was a clear interest in having a better assessment of present-day seismic signal detection capabilities. Issues of detectability are at the center of discussions on seismic monitoring because they define thresholds below which either there will be no data at all on which to make judgements or the data will be so sparse that the answers to crucial questions are unreliable. As a result of the discussions several groups of seismologists agreed to collaborate in an informal way in putting together a new assessment of detection capability. This short report describes the techniques used in the study and the first results to emerge from it.