The sites of schizogony of Plasmodium falciparum in deep vascular tissues were evaluated in two Aotus trivirgatus, night monkeys. The experiments were performed 3 and 4 days after inoculation, when 1 to 2% of the red cells contained parasites. At this time peripheral blood films, organ crushes, and tissue-section of the organs were made. The mature trophozoites and schizonts were concentrated in the same organs. The major sites included the ventricle and atrium of the heart, adipose tissue, skeletal muscle, and the submucosa of the small intestine. The parasitized red cells lined the veins and, to a lesser extent, the capillaries in the involved organs. Most schizonts in the spleen appeared abnormal. This infection is compared with that caused by Plasmodium coatneyi, in monkeys, in which the schizonts are also concentrated in heart and adipose tissue. Unlike P. falciparum, the schizonts of P. coatneyi have a higher density in liver and lung than in peripheral blood. A possible relation between deep-vascular schizogony and the complications of malignant falciparum malaria was discussed.