Seventeen adult patients with acute Plasmodium falciparum malaria, admitted to the Hospital for Tropical Diseases, were studied. Serial measurements of the serum concentration of C-reactive protein, serum amyloid A protein, and percentage parasitaemia were determined, together with initial measurement of serum electrolytes, liver function, haemoglobin, white cell and platelet counts. Initial C-reactive protein and serum amyloid A concentrations were increased (C-reactive protein mean 49.0 mg/l serum amyloid A 28 mg/l) falling towards the normal range by the seventh day of treatment. There was a significant correlation between the pretreatment parasite count and clinical and laboratory markers of inflammation. C-reactive protein and serum amyloid A concentrations correlated inversely with the serum sodium. These results indicate that measurement of acute phase reactants such as C-reactive protein and serum amyloid A may prove valuable in assessing the severity of P falciparum malaria, and in following the response to antimalarial treatment.