The late Paleocene thermal maximum (LPTM) was a dramatic, short-term global warming event that occurred ~55 Ma. Warming of high-latitude surface waters and global deep waters during the LPTM has been well documented; however, current data suggest that subtropical and tropical sea surface temperatures (SSTs) did not change during the event. Conventional paradigms of global climate change, such as CO2-induced greenhouse warming, predict greater warming in the high latitudes than in the tropics or subtropics but, nonetheless, cannot account for the stable tropical/subtropical SSTs. We measured the stable isotope values of well-preserved late Paleocene to early Eocene planktonic foraminifera from South Atlantic Deep Sea Drilling Project (DSDP) Site 527 to evaluate the subtropical response to the climatic and environmental changes of the LPTM. Planktonic foraminiferal Δ18O values at Site 527 decrease by ~0.94? from pre-LPTM to excursion values, providing the first evidence for subtropical warming during the LPTM. We estimate that sub-tropical South Atlantic SSTs warmed by at least ~1¿--4 ¿C, on the basis of possible changes in evaporation and precipitation. The new evidence for subtropical SST warming supports a greenhouse mechanism for global warming involving elevated atmospheric CO2 levels. ¿ 1999 American Geophysical Union