We investigated spontaneous cytokine production in two patients with pure red cell aplasia (PRCA). The peripheral blood mononuclear cells (PBMNC) from two patients produced IL-2. Cyclosporin A (CyA) suppressed in vitro IL-2 production in one patient, but not in the other. Spontaneous IL-2 production disappeared in one patient 10 months after the start of CyA therapy. The patient for whom CyA therapy was stopped after the disappearance of spontaneous IL-2 production has remained in continuous remission for 1 year. The present case suggests that spontaneous IL-2 production in PBMNC might be an indicator of disease activity.