The ultrastructure of three cases of fatal human falciparum malaria was studied in order to identify the cytoadherence of the endothelial cells in relation to parasitized red blood cells and septal interstitial changes which could be related to respiratory distress. Two cases showed marked endothelial oedema narrowing the capillary lumen with areas of adherence preferentially related to knobs, accompanied by septal interstitial oedema. One case showed no endothelial cells oedema, no knobs in parasitized red blood cells with no cytoadherence, no septal interstitial oedema and no respiratory distress. Cytoadherence seems to be the mechanism responsible for the septal pulmonary changes in severe falciparum malaria.