To the Editor.— We have always recognized the difference in treatment of the asexual and sexual forms of malaria. People forget that the asexual forms of Plasmodium falciparum malaria parasites have a 48-hour cycle as compared to a ten-day or two-week cycle for gametocytes. The fundamental reason for the failure of quinine, quinacrine (Atabrine), and chloroquine to eliminate the gametocytes is their inability to kill the schizonts of the gametocytes. Obviously these drugs clear the asexual forms, and relieve the clinical symptoms ( 215 :291, 1971). The only real significance of the retained gametocytes is the Public Health problem, particularly in endemic areas. This has been well pointed out by Drs. Berman and Holmes, and their report of the successful treatment of the gametocytes with primaquine in limited dosage is certainly a step forward. We have known from the beginning that primaquine clears the blood of gametocytes, but the important point