Site 275 of the Deep Sea Drilling Project is located in the South Pacific, at the southeast margin of Campbell Plateau, on a relatively elevated bottom eroded by bottom currents. Under a thin layer of Recent-Pleistocene foraminiferal ooze, Late Cretaceous siliceous sediments were drilled: a bright-yellow upper unit is 14.5 m thick and is underlain by a dark-brown unit down to 62.0 m. At this depth further drilling was prevented by hard siliceous shale. The two units are distinctly different both lithologically and paleontologically. Unit 1, down to 14.5 m, consists of diatom-radiolarian ooze with abundant siliceous microfossils, mostly of cold-water oceanic plankton, such as Archaeomonadaceae, Diatomaceae, Radiolaria, Silicoflagellatae, with accessory sponge spicules. Microfossils make up 60-90% of the sediment. The underlying Unit 2 consists of olive-gray partly detrital clayey silt with thin intercalcations of lithified siliceous shale. It yielded Radiolaria, Dinoflagellata, and colonies of green algae, but no Archaeomonadaceae, Diatomaceae, or Silicoflagellatae. The microfossil assemblages of 21 samples from cores 1 and 2 of Unit 1 were examined and evaluated in detail. Thus far, 158 species have been determined, including 4 new genera, 57 new species, and 3 new combinations, all extinct. The sediment is of Late Cretaceous age. Based on the abundance and vertical ranges of the species, 9 biozones and 12 subzones have been established.