From April through December 1967, the R/V ARGO of the Scripps Institution of Oceanography took part in Expedition NOVA, a detailed geological and geophysical study of the southwest Pacific. On June 23 and 24 two major seamounts, which have been named Hohnhaus and Dixon seamounts, were discovered about 104 km apart on the abyssal plains of the central Pacific. The northernmost, Hohnhaus seamount, is located at 13 degrees 30'N, 179 degrees 10'W; a single crossing was made which showed that it is at least 3780 m high with a base diameter greater than 50 km. Dixon seamount, located at 12 degrees 34'N, 179 degrees 05'W, was subjected to an extensive topographic, subbottom reflection, and magnetic survey. It is 4100 m high, 63 km wide at its base, and rises with the 20 percent slope characteristic of shield volcanoes from the surrounding abyssal plain mean depth of 5700 m to a minimum depth of 1581 m. The topography was surveyed with a standard Gifft Depth Recorder; a towed free-precession magnetometer gave the total magnetic field intensity along the ship's track and subbottom reflection profiles were obtained using an air gun sound source.