Balance between inflammatory and anti-inflammatory cytokines may be important in malaria presentation and outcome. To clarify cytokine interactions that produce pathology of malaria and control infection, C57BL/6 mice were infected with 10(4) parasitized RBCs from a non-lethal strain of Plasmodium yoelii. Kinetics was monitored showing the course of parasitemia, and cytokines were determined by RT-PCR from liver and spleen tissues. Inflammatory cytokines such as interferon-gamma (IFN gamma), interleukin (IL)-12, IL-6, tumor necrosis factor-alpha (TNF alpha) and anti-inflammatory cytokines, including IL-4 and IL-10, were investigated as key molecules that interact with immune cells in the activation of the immune responses. The production of IFN gamma mRNA was found to be higher on day 7 than on day 21 after infection, and IL-12 and IL-6 showed higher expression in the liver than in the spleen. Though TNF alpha was highly expressed on day 14 after infection and on day 21 in the liver, such expression was decreased on day 21 in the spleen. Anti-inflammatory cytokines showed high expression in both the liver and spleen. The results suggest that a relative balance between inflammatory and anti-inflammatory cytokines is crucial and that the increase of inflammatory cytokine levels during the acute phase of malaria may reflect an early and effective immune response. The counteraction effect of anti-inflammatory cytokines is thought to play a role in limiting progression from uncomplicated malaria to severe life-threatening complications.