Analysis procedures and instrumentation to measure low levels of sulfur hexafluoride in seawater are described. The minimum detectable level for a 500 mL sample is about 3¿10-17 mol/L. Concentrations from 1.5 to 300¿10-15 mol/L can be measured with approximately 2% precision. The procedure includes a concentration step employing a trap of Porapak-Q¿ in a dry ice/2 propanol bath. The system has been used for tracer experiments in Santa Monica Basin and Santa Cruz Basin, and will be improved for future tracer release experiments in the deep ocean. ¿1991 American Geophysical Union