Six patients with Rheumatoid Arthritis (RA) have been treated with lymphocytapheresis after their disease proved unresponsive to conventional therapy. Clinical improvement, measured evaluating articular swelling, morning stiffness, and muscle weakness, was observed in four of the six patients. From the cellular point of view lymphocytapheresis induced (1) T cell depletion without modification of lymphocyte subsets in the peripheral blood, (2) improvement of lymphocyte responsiveness to lectins, autoantigens and alloantigens. All together these data suggest that therapeutic leukapheresis modifies the immune responsiveness in humans, possibly facilitating the process of cell to cell cooperation.