the cytokine tumor necrosis factor and other as yet unidentified factor(s) which together mediate the killing of intraerythrocytic malaria parasites are transiently elevated in sera during paroxysms in human plasmodium vivax infections in non-immunes. these factors which included tnf and parasite killing factor(s) are associated with the clinical disease in malaria to the extent that their transient presence in infection sera coincided with paroxysms, the most pronounced clinical disturbances of p. vivax malaria and secondly because their levels were markedly lower in paroxysm sera of semi-immune patients who were resident of an endemic area. further, a close parallel was obtained between serum tfn levels and changes in body temperature that occur during a p. vivax paroxysm in non-immune patients, suggesting a causative role for tnf in the fever in malaria. p. vivax rarely if ever cause complicated clinical syndromes. nevertheles serum tfn levels reached in acutely ill p. vivax patients were as high as in patients suffering from cerebral complications of p. falciparum malaria as reported in studies from the gambia. cytokine profiles and other changes accompanying clinical disease in p. vivax and p. falciparum malaria are compared in this paper with a view to discussing the potential role of cytokines in the causation of disease in malaria.