The distribution of cobalt was determined at one station in the oligotrophic western Philippine Sea that is far removed from the direct influence of any major land mass. Concentrations of cobalt (> 95 pM) in the top 150 m of water in and above the thermocline were much higher than those (about 25 pM) in the deep waters below 1000 m. Since no major river drained directly into the study area, these elevated concentrations in the surface waters could not have been sustained by a riverine input. A more likely source of cobalt to these waters might have been atmospheric deposition. Below 150 m, as a first approximation, the relationship between cobalt and salinity mimicked that between potential temperature and salinity with inflection points occurring at about the same depths. Thus, the distribution of cobalt in these deeper waters was governed primarily by mixing processes. Within the top 150 m, a subsurface maximum, centered around 48 m, was found in the shallow halocline. This maximum might have resulted from the preferential trapping and re-mineralization of particles in a strong pycnocline.