This paper from the Malaria Research Division, Institute for Medical Research, Federation of Malaya, summarizes the results of studies on the suppression of malaria by synthetic drugs. Such studies began 25 years ago, and, in spite of interruptions in the work due to the Japanese invasion and due to banditry, studies are reported here on the effects of giving mepacrine in doses of 0.3 gm. once a week; proguanil in doses of 0.1 gm., 0.2 gm., 0.25 gm. and 0.3 gm. once a week; chloroquine in doses of 0.25 gm. once a week; and amodiaquin [camoquin] in dosos of 0.4 grn. base once a month. The populations upon whom the studies were made were labourers and their families-Tamils, Malays, and Javanese, on 3 estates in Selangor, and Negri Sembilan, Federation of Malaya, between December, 1946, and February, 1949. Each population was divided into 3 comparable sections, 2 of which received test drugs, while the third received a placebo and so formed a control group. Drugs were issued under the supervision of a Malaria Research Officer. Those people who developed fever wore supervised and treated by a hospital assistant resident on each estate. Thick blood films from such patients were studied. Parasite and spleen surveys were done every 3 months. Malaria transmission was assessed by the incidence of malaria in unprotected infants, who were not given suppressive drugs until after their first attack; and by the results of mosquito dissections. The commonest vectors woreA. letifer, A. maoulatus and A. umbrosus. The results of the tests of suppressivo drugs are shown in a series of tables, charts, and diagrams. Malarial transmission was considered light during the period of these trials. Chloroquino 0.25 gm. base once weekly proved the most effective drug in suppressing malarial attacks. There was little difference between proguanil in various doses, or between proguanil and mepacrine, but these two drugs were much cheaper than chloroquine or amodiaquin. All the drugs reduced the parasite and spleen rates. No significant toxic symptoms were observed with any of the drugs used. S. Bell.