Temperature-diagnostic nannofossil species have been used in an attempt to identify trends in surface-water changes in the Woodlark Basin during the Pliocene. The relative abundance of warm-water Discoaster brouweri compared to cool-water Coccolithus pelagicus is a useful proxy for interpreting Pliocene surface-water temperature trends at Ocean Drilling Program Site 1115 (Woodlark Basin in the Solomon Sea). Surface waters were mostly warm during the early Pliocene with a slightly cooler interval centered on 4.5 Ma. A more pronounced cool interval occurred at about 3.2 Ma. The early and middle Pliocene cool periods may reflect Antarctic glacial growth. A mid-Pliocene warm interval occurred from about 3.1 to 2.8 Ma, followed by a long-term decline in surface-water temperatures beginning about 2.7 Ma. This event probably correlates to the onset of Northern Hemisphere glaciation. Cooling continued to the end of the Pliocene, with a brief influx of warmer water appearing at about 2.3 Ma.