Human lymphocytes were cultured in vitro with multiple concentrations of antigen [streptokinase-streptodornase], mitogen [phytohemagglutinin M] and allogeneic cells. The addition of levamisole [useful in secondary chemotherapy of cancer] to stimulated cultures in concentrations of 0.03-33 .mu.g/ml significantly amplified the response of lymphocytes to these stimuli with little or no effect on control cultures. The combination of stimulus and levamisole concentration which produced amplification was unique for each individual culture. The inconsistent results found here and elsewhere may reflect instability of levamisole under conditions of the in vitro lymphocyte culture system. [This drug improved the responses of some advanced cancer patients to challenge with the contact allergen dinitrochlorobenzene.].