The regulation of the migratory capacity of Percoll-purified large granular lymphocytes (LGL) into nitrocellulose filters was studied in a 2-hr assay with the use of modified Boyden chambers. Compounds that stimulate the natural killer cytotoxic function of LGL, such as interferons (natural beta, recombinant alpha A, recombinant hybrid alpha A/D, recombinant gamma), recombinant interleukin-2, and inactivated streptococci (OK 432), augmented the capacity of LGL to penetrate into filters spontaneously in the absence of chemoattractants in the lower compartment of the chamber. These compounds did not increase the LGL responsiveness to chemoattractants. Phorbol 12-myristate 13-acetate did not appreciably affect the locomotory capacity of LGL but augmented their cytotoxic activity. Thus the cytotoxic function and locomotion of LGL in response to biological response modifiers can be dissociated.