The distribution of dissolved gaseous mercury (DGM) was determined at four hydrographic stations in the tropical Pacific Ocean. These vertical profiles of DGM, to a depth of 400 meters, are the first obtained for the open ocean. Dissolved gaseous Hg concentrations generally increased with depth. The major portion of DGM in surface sea water was of an inorganic gaseous form, probably elemental Hg (Hg¿). In two instances, organic gaseous Hg, presumably dimethyl Hg [(CH3)2Hg>, was observed in the deeper waters. These results suggest that bacteria may be responsible for producing Hg¿ and (CH3)2Hg at depth in this ocean region. ¿ American Geophysical Union 1988