Real-time holographic interferometry, previously used to measure concentration profiles in the polarized layer during membrane processes, has been applied to visualize the buoyancy effects on dead-end reverse osmosis of salts by rotating the cell 90 degrees and 180 degrees from its original position (0 degrees). Sets of experiments have been carried out, each one with the membrane in a different gravitational orientation, using NaCl and Na2SO4 with a feed concentration ranging from 1 to 7 kg/m(3) at a constant pressure of 600 kPa. The interferometric fringe patterns obtained in each membrane position were very different. At the 0 degrees position, the evolution of the polarization layer was observed by means of several interferometric fringes parallel to the membrane surface. At 180 degrees position, the interferometric fringe pattern obtained pointed out the existence of a natural convection or buoyancy flow in the vicinity of the membrane surface which prevented the growth of the polarization layer. Finally, with the membrane vertically placed, an intermediate situation occurred. The combination of the diffusive movement of the solute (horizontal) and the natural convection currents (vertical) caused by the density gradient established in the module produced deformations on the interference fringes. The main consequence of the buoyancy effect is a great enhancement of the membrane performance and, therefore, a higher effectiveness of the reverse osmosis process.