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The Lombok Strait, a gap in the lower Indonesian Archipelago second in cross sectional area only to the Timor passages, provides a major pathway for the Pacific to Indian throughflow. A global reduced gravity model, corroborated by dynamic height climatology from the Generalized Digital Environmental Model, predicts annual mean sea levels 15-20 cm higher at the Pacific entrance to the Indonesian Seas than in the Indian Ocean south of the archipelago straits. Consistent with this regional pressure gradient, Pacific core layers of the Northern Subtropical Central Water and the North Pacific Intermediate Water are traced southward from the Makassar Strait into the Lombok Strait. Maps of temperature, salinity, and density distributions and sea surface dynamic heights in the Lombok Strait from January, June, and September 1985 also indicate a persistent southward flow of appreciable magnitude. Geostrophic speeds, however, are clearly too large by a factor of two or more. Current meter arrays in the north strait (January 1985 – March 1986) provide direct measurements of southward currents which persist through most of the year and are concentrated in the upper few hundred meters consistent with Wyrtki’s (1987) analysis of the regional pressure gradient. Maximum sustained speeds of over 70 cm/sec occur from July to September with a long period of weak currents from mid-October 1985 through January 1986. Tropical cyclones in the Timor Sea (December-April) force strong northward flow reversals which can persist for ten days. The wind-forced numerical model identifies the strong westward wind stresses in the Timor Sea during the southeast monsoon as the major cause of the annual cycle of current in the Strait.