This volume covers Leg 85 of the cruises of the Drilling Vessel Glomar Challenger. When DSDP developed the hydraulic piston corer (HPC), it became possible to recover fairly undisturbed samples from the upper 100 to 300 m and thus to carry out high resolution stratigraphic studies. DSDP Leg 85 was designed to take advantage of this capability. A modified HPC (the VLHPC—variable length hydraulic piston corer) and rotary coring were to be used to recover complete, undisturbed equatorial Pacific sections. The biostratigraphy, magnetostratigraphy, and seismic, carbonate, and stable isotope stratigraphy of these sections were to be studied to develop a better understanding of the paleoceanographic and paleoclimatic history of the region. The JOIDES Ocean Paleoenvironment Panel selected five drill sites that would best address the Leg 85 objectives. Two sites (571 and 572) are in the eastern Pacific, and the three others (573, 574, and 575) form a north-south line that lies at approximately 133°W across the equatorial high productivity zone. The drilling at all five sites was expected to result in the recovery of "reference" sections for the study of foraminifers, nannofossils, radiolarians, diatoms, and other fossils. A secondary objective was to make a detailed examination of the relationships between paleoceanographic changes and the acoustic and physical properties of the sediments. Understanding these relationships could substantially increase the ability to use seismic stratigraphy as a paleoceanographic tool. Another secondary objective was to conduct an in situ heat flow and pore water experiment to study pore water advection in a region of unusually low heat flow (Site 571). Leg 85 began in Los Angeles, California in March 1982 and ended in Honolulu, Hawaii in April 1982.