Centro Andaluz de Biología Molecular y Medicina Regenerativa (CSIC) 1 article published in JoVE Immunology and Infection Image Processing Protocol for the Analysis of the Diffusion and Cluster Size of Membrane Receptors by Fluorescence Microscopy Carlos Oscar S. Sorzano*1,2, Laura Martínez-Muñoz*3,4, Graciela Cascio3,5, Eva M. García-Cuesta3, J. Vargas1,6, Mario Mellado3, Jose Miguel Rodriguez Frade3 1Department of Macromolecular Structures, Centro Nacional de Biotecnología, Campus Univ. Autónoma de Madrid, 2Campus Urb. Montepríncipe s/n, Univ. San Pablo CEU, 3Department of Immunology and Oncology, Centro Nacional de Biotecnología, Campus Univ. Autónoma de Madrid, 4Department of Cell Signaling, Centro Andaluz de Biología Molecular y Medicina Regenerativa (CSIC), 5Meyer Cancer Center, 6Department of Anatomy and Cell Biology, McGill Univ. Here, we present a protocol for single particle tracking image analysis that allows quantitative evaluation of diffusion coefficients, types of motion and cluster sizes of single particles detected by fluorescence microscopy.