The purpose of this study was to evaluate nitric oxide (NO) activity in patients with uncomplicated malaria. Lipopolysaccharide and gamma interferon (IFN-gamma) are potent inducers of NO by inducing production of NO synthase. NO activity was determined by measuring serum levels of nitrite/nitrate (metabolic end products of NO), and IFN-gamma in patients with uncomplicated malaria, mostly caused by Plasmodium falciparum. Neither serum levels of nitrite/nitrate nor of IFN-gamma were significantly increased in patients with uncomplicated malaria, especially in patients with P. falciparum infection, and in those with high parasitaemia. These results show that NO cannot play a role in uncomplicated malaria, and it is still debatable if NO production in this infection has beneficial or detrimental effects.