Halpern's colloidal-carbon method was used to measure nonspecific phagocytic activity in rats infected with Plasmodium berghei, in rats infected and treated with amodiaquine or chloroquine, and in uninfected rats, some of which were treated with amodiaquine or chloroquine. The drugs did not modify phgocytosis of carbon in malaria-free rats. In malaria-infected rats, the drugs hastened the return of the phagocytic system to its control state. The changes in spleen, liver, and lung weight as well as hematocrit and parasitemia during the course of untreated and treated infections were compared with the changes in nonspecific phagocytic activity. We conclude that chemotherapy and phagocytosis are independent factors in the suppression of berghei malaria. These results are in harmony with previous observations of others, who studied the effects of quinine against Plasmodium gallinaceum.