Proper intracellular cholesterol transport is critical for various cellular functions and any abnormality can lead to several fatal diseases such as atherosclerosis, cholelithiasis, and Alzheimer disease. Nowadays a complete understanding of cholesterol transport behaviour in cells remains elusive. Various studies have been done in vitro and in vivo to explore the cholesterol transport properties, but none of them was conclusive about the process time-scales. Recently we showed that it is possible to follow the inter- and intra-membranes cholesterol transport by time resolved SANS measurements. We now propose to study the overall exchange kinetics of cholesterol-sulfate in POPC and d54DMPC deposited bilayers by means of neutron reflectometry, following the methodology already used in two recent INTER experiments (RB1120426 and RB 1220206).