We investigated the levels of 6 different cytokines in the sera of 10 newly diagnosed patients with B cell lineage acute lymphoblastic leukemia (ALL) and detected a significant increase in IL-6 and IFN-alpha serum levels in comparison to that of healthy controls. Whole blood cell cultures of 10 ALL patients and 20 control individuals were induced with classical cytokine inducers, such as virus, PHA and LPS, and their ability to produce 9 different cytokines was compared. Blood cells of ALL patients produced significantly less IL-1alpha, IL-1beta, IL-10 and TNF-alpha than control cells and not significanly lower levels of IL-6, but comparable with control levels of IL-2, IL-4. rHuGM-CSF added to cell cultures 24 h before induction significantly enhanced the production of IL-1alpha, IL-1beta and TNF-alpha in controls, but only IL-1alpha and IL-1beta in the blood cell cultures of patients with ALL. GM-CSF did not significantly influence the production of IFN-alpha, IFN-gamma, IL-2, IL-4 and IL-10 in the control cells and the cells of ALL patients. The patients examined differed not only in the expression of CD10 and CD34 antigens on blast cells, but also in the reaction to GM-CSF treatment, which was found as very high standard deviation values. We suppose that these differences can partially explain the different effects of GM-CSF when used to ameliorate neutropenia of ALL patients after chemotherapy and to reduce the incidence of microbial infections.