A system, using a cooled slow-scan charge coupled device camera attached to a fluorescence microscope, allows a series of images to be stored, up to 500 fluorescent spots (labelling particles) per image can be identified by position and intensity. The movement of the spots can be traced. The tracking method allows the mobility to be analysed. The receptors of influenza virus and low density lipoprotein on fibroblast have three different types of motion: random motion, directed motion and motion limited to a domain. The high sensitivity of the system leads to short exposures and little photobleaching during the observations. The measurement principle of this system and its biological applications were described.