Pacific subtropical-tropical thermocline water exchange is estimated using the National Centers for Environmental Prediction oceanic general circulation model in which observed temperatures are assimilated. In the main thermocline (23<&sgr;t<26.2), the equatorward exchange transports are about 17 Sv (1 Sv=106 m3s-1) and 26 Sv at 10 ¿N and 10 ¿S, respectively. Consistent with observations and other model simulations, the water exchange has a Low-Latitude Western Boundary Current (LLWBC) pathway and an interior pathway. The equatorward LLWBC and interior transports are about 14 and 3 Sv, respectively, at 10 ¿N and are about 15 and 11 Sv, respectively, at 10 ¿S. The time required for subtropical water to penetrate into the equatorial ocean is usually less than 10 years. Exchange windows are also identified in both the North and South Pacific. ¿ 1999 American Geophysical Union