Direct measurements of buoyant plume wafers collected by submersible show that the behavior of Al is highly nonconservative during the early mixing of submarine hydrothermal fluids and seawaters at the TAG and MARK sites on the Mid-Atlantic Ridge. Al is removed from the hydrothermal end-members and is also stripped from the entrained seawater to produce levels of Al in the plume solutions about one fifth of normal seawater concentrations. The behavior of Al appears to be similar to that inferred for other anionic species (V, As, Cr, P) which exhibit constant element-iron ratios in hydrothermal plume particles and suggests that such elements are removed from seawater during the early stage of formation of hydrothermal plumes. ¿ American Geophysical Union 1993