Niobium and tantalum were measured in North Pacific seawater. The concentration of Nb shows a slight depletion in surface water and that of Ta shows a slight increase near the bottom. The mean concentrations of Nb in surface and deep Pacific water are 3.0 and 3.8 pmol/kg, respectively, and for Ta, 0.08 and 0.20 pmol/kg. Their relatively uniform distribution suggests that Nb and Ta are less reactive with particles in seawater than Zr and Hf. In analogy with V, the species of Nb and Ta may be oxyacids rather than hydroxides. ¿ 1998 American Geophysical Union