Interaction of anti-immunoglobulin antibodies with the surface Ig of B lymphocytes leads to capping and endocytosis of the immune complexes and to a brief stimulation of translational motility. Lymphocytes are not stimulated to move by interaction with other ligands, such as antibodies to the theta isoantigen, to H2 determinants, or to determinants recognized by heterologous anti-lymphocyte antibodies. Furthermore, anti-lymphocyte antibodies block the motility produced by anti-Ig. This effect was not seen in cells treated with colchicine, suggesting that the antilymphocyte effect may be associated with hyperstabilization of microtubules. Finally, we report on preliminary experiments using chemotactic chambers which show that anti-Ig stimulates random but not directional movement.