One of the most controversial problems of glacial paleoclimatology is the conservative change in tropical sea surface temperature (SST) in contrast with the large high altitude temperature change in the western tropical Pacific. In this report SST was estimated for the last 20,000 years using alkenones preserved in marine sediments recovered from a site 800 km north of New Guinea. The UK37 (unsaturation degree of long-chain alkenones synthesized by planktonic prymnesiophyte algae) record suggests that SST decreased at most 1.5 ¿C at the last glacial maximum. This small changes in SST of the western tropical Pacific is concordant with results previously reported in UK37 studies from the eastern equatorial Pacific and the equatorial Atlantic. The UK37-based SST estimates are in good agreement with the CLIMAP results and plaktonic foraminifera Δ18O, but much smaller than those (ca. -5 ¿C) obtained from coral Sr/Ca and Δ18O thermometries and glacial vegetation reconstruction. ¿ American Geophysical Union 1994