Research on protein-membrane interactions has been undeveloped due to the lack of proper techniques to detect the position of proteins at membranes because membranes are usually only about 4-nm thick.We have recently developed a new method named surface-induced fluorescence attenuation (SIFA) to track both vertical and lateral kinetics of a single labelling dye in supported lipid bilayers.It takes advantage of strong interaction between a light-emitting dye and a partially reflecting surface.By applying the technique to membrane proteins being fluorescently labelled at different residues,here we show that SIFA can measure not only the insertion depth of a dye inside a lipid bilayer,but also the position of a dye in solution near the surface.SIFA can therefore be used to study membrane proteins of various types.