Hairy cells (HCs) and some activated B cells express high levels of macrophage colony-stimulating factor (M-CSF) (CSF-1) receptor, but the functional effects of the cytokine on B cells have not been previously identified. Using video microscopy, image analysis, and migration assays, M-CSF was shown to induce chemokinetic and chemotactic movement of HCs. This movement response involved transition to a highly mobile, rounded cell form and was accompanied by distinctive changes in F-actin polymerization and distribution. Furthermore, the M-CSF-induced motility was substantially modified by the adhesive protein used as a substratum and involved qualitative changes in the function of the alpha v beta 3 integrin of HCs. It is suggested that the findings are relevant to the pathophysiology of hairy-cell leukemia (HCL) in particular, and to the biology of B-cell migration in general.