In order to decipher past variations in sea-surface temperature in the western equatorial Pacific Ocean, the relative abundances of planktic foraminifera from Ocean Drilling Program Site 806 have been analyzed from the time interval 3.9-2.4 Ma. Pliocene sea-surface temperatures were estimated from the planktic foraminiferal data using transfer function FP-12E and the modern analog technique. Results from these two methods indicate cooler sea-surface temperatures between approximately 3.35 and 3.05 Ma using the modern analog technique, and between 3.35 and 3.2 Ma and approximately 3.15 and 3.0 Ma using transfer function FP-12E. The apparent cooler periods coincide partly with an increase in planktic and benthic foraminiferal δ18O. Comparison between estimated sea-surface temperatures and species abundances indicate that the estimated changes in sea-surface temperature during this period could be the result of changes in the depth of the thermocline rather than a decrease in sea-surface temperature.