Twelve Rhesus monkeys were inoculated intravenously with about 500 000 malaria parasites, Plasmodium knowlesi. Acute hemolysis occurred 5 days later, and all animals died on the 6th or 7th day after inoculation. All organs were gray-green to gray-brown because of deposition of hemoglobin and malaria pigments. This deposition was particularly striking in the lung, brain, abdominal fat and serous surfaces. Microscopic changes indicative of acute hypoxia were found in the liver (centrilobular necrosis) and kidneys (acute tubular necrosis). Terminal intravascular coagulopathy was evidenced by widely distributed, recently formed, fibrin thrombi.