Geochemical Ocean Sections Study (GEOSECS) Indian Ocean Expedition data show that silica and 3He in the Red Sea Deep Water are linearly correlated, suggesting a common hydrothermal source. Silica sections for the Red Sea from the GEOSECS and Mer Rouge (MEROU) expeditions show a strong vertical silica maximum centered at 500 to 600 m depth. The MEROU sections, which have higher horizontal resolution than the GEOSECS sections, suggest that the primary silica source lies in the south at that depth. The interpretation is that the large-scale silica and 3He distributions are due to the dispersal in the Red Sea Deep Water of warm or hot hydrothermal vent waters associated with the seafloor spreading center of the southern Red Sea. The helium- and silica-rich hot brines of the central Red Sea probably cannot provide the large fluxes of silica or 3He required to maintain the inventory of either of these deep water properties in steady state. The hypothesis of a common hydrothermal source for silica and 3He can most readily be tested by measurements of the germanium-silicon ratio in Red Sea Deep Water. ¿ American Geophysical Union 1996