Polarographic measurements showed that Catechol complexes of vanadium(V) adsorb onto the hanging mercury drop electrode. This property forms the basis of a sensitive eiectrochemical technique by which dissolved vanadium in seawater can be determined directly. The reduction current of adsorbed complex ions of vanadium is measured by differential pulse cathodic stripping voltammetry, preceded by a period of collection of a few minutes. The peak potential Is at --0.7 V. Optimal experimental parameters were found to be a catechol concentration of 2 X IO-* M, a collection potential of -0.1 V, and a soiutlon pH of 6.9. The limit of detection is 0.3 nM vanadium after a 2-min collection with a stirred soiutlon, which is decreased further to 0.1 nM after a 15-min collection.