The development and functional activities of B lymphocytes critically depend on their migratory capacity. Both in vitro and in vivo assays can be used to assess the migratory ability of B cells. Filter-based transwell assays measure both spontaneous and chemoattractant-induced cell migration in vitro. Flow cytometric analysis of labeled cell subsets present in the input and migratory cells from transwell assays allows the assessment of the migratory capacity of specific cell types in a complex mixture of cells. A similar approach can be used to assess the migratory capacity of B cells transfected with a green fluorescent fusion protein. Despite the success of the transwell assay, attempts to image directionally migrating B cells have been limited. The assessment of the in vivo migratory capacity of genetically modified or pharmacologically treated B cells usually involves their adoptive transfer into recipient mice. The localization of transferred cells in lymphoid organs can be determined by immunohistochemistry and/or flow cytometric analysis of harvested tissues or cells. Because the proper localization of B cells in lymphoid organs is a multistep process, abnormal positioning can occur even in the absence of an intrinsic defect in cell migration.