Diatom-rich ooze from ODP Leg 177, Site 1090, Hole 1090B, was examined for biogenic silica weight percentages. Site 1090 is located between the Cape of Good Hope and Antarctica (42 degrees 54.821'S, 8 degrees 53.984'E). Sampling in Hole 1090B was spaced at approximately 10 cm intervals, with a temporal resolution of 10-30 ka. Analysis involved samples between 240 and 283 mcd. Biogenic silica was extracted from sediments by alkaline solution per the method of Mortlock and Froelich (1989), with minor modifications. Measurement of biogenic silica weight percentages was determined using molybdate-blue spectrophotometry. The focus of this study is the Eocene-Oligocene boundary. Hole 1090B spanned the Eocene-Oligocene boundary at 33.7 Ma at a depth of 268 mcd. Biogenic silica weight percentages did not vary significantly across this boundary. Changes 1-2 Ma above the boundary may reflect carbonate dissolution events. Climatic variation near this transition has been linked to Milankovitch cyclicity. Analysis by FFT and visual methods showed that the biogenic silica measured in this study had weak variation at 400 and 100 ka intervals. The most striking feature of these sediments is an unexpected dramatic drop in sedimentation and mass accumulation rates just above the Eocene-Oligocene boundary at 33.7 Ma.