Polymorphonuclear leukocytes from patients with psoriasis demonstrated a significantly enhanced chemotactic responsiveness to zymosan-activated human serum as compared to granulocytes from healthy volunteers. Furthermore, psoriatic peripheral blood mononuclear cells stimulated with concanavalin a produced an increased amount of lymphocyte derived chemotactic factor (LDCF) as compared to that in the case of healthy persons. The LDCF proved to be chemokinetic for the psoriatic granulocyte. It is postulated that these two phenomena may play a role in the pathogenesis of psoriasis.