Although this paper makes a special appeal to workers in Malaya it will be found interesting and instructive by the many medical men elsewhere who have been perplexed by the confusing nomenclature of rats and related animals. The author describes the following, which are the six common house and field animals of Malaya popularly called "rats ". A. Rodentia: Muridae. (1) Rattus rattus (Sp. R.r. diardi; R. r. argentiventer; R. r. jalorensis. (2) R. norvegicus. (3) R. exulans. (4) Mus musculus. (5) Bandicota bengalensis. B. Insectivora: Soricidae. (6) Suncus caeruleus, the musk shrew which is grossly slandered by being called a rat; it is an insectivore and the author states that there is no evidence of its being concerned in the transmission of any disease. A clear description is given of the habits, external appearance, skull characters, and association, if any, with disease, of each of the above animals. The animals chiefly concerned in the transmission of disease in Malaya are stated as being R. r. diardi (murine typhus), and R. r. argentiventer, (scrub typhus and probably leptospirosis). Plague is not occurring at present in Malaya. Medical men in Malaya are fortunate in being provided in this and other papers with simple practical guides to the local fauna which are important from the public health point of view. [See also this Bulletin, 1949, v. 46, 245, 247.] John W. D. Megaw.