During the recent war an intensive search for new antimalarial drugs was conducted in the course of which thousands of chemical substances were investigated under the auspices of the Office of Scientific Research and Development. Studies were designed to find drugs which might have one or more of the following properties: (a) true causal prophylaxis, (b) ability to effect complete cure following treatment, (c) greater efficacy than quinacrine and quinine in suppression and (d) greater efficacy than quinine and quinacrine in the treatment of acute clinical attacks. The present report is concerned with chloroquine (SN 7618): 7-chloro-4-(4-diethylamino-1-methylbutylamino) quinoline, which is one of a series of new active antimalarial agents. Detailed studies of the antimalarial properties, pharmacology and toxicity of this drug have been carried out by numerous investigators, and undoubtedly the results of these studies will be generally available in the near future.1 This paper is concerned principally with