During the last five years a good deal of information about the detailed distributon of Malayan rats has been gathered in connection with studies on trombiculid mites carried out at the Institute for Medical Research, Malaya. By methods of trapping and marking rats in a variety of habitats some of their preferences have been worked out. Information on these habitat preferences is given for the following rats: Rattus rattus diardi, R. r. jalorensis, R. r. argentiventer, R. exultans, mülleri, rajah, whiteheadi and sabanus: and some notes on R. norvegicus, annandalei and bowersi.

The infestation by trombiculid mites is used as evidence that rats do or do not share the same micro-habitat, since these mites have no marked host preferences.

Evidence is adduced that Rattus rajah surifer and R. r. pellax are probably but colour varieties of the one species.