The present article is an outline of biological studies of inland waters in Southeast Asia with especial reference to those conditions which limit the adequacy of our knowledge thereof. The most detailed limnological knowledge was obtained by the German Limnological Sunda Expedition, 1928-29,which was undertaken by Thienemann and Ruttner in the islands of Sumatra, Java and Bali. In countries both insular and continental other than those islands, despite the work of many biologists and limnologists our knowledge is still inadequate even for the taxonomy and biogeography of animals and plants in inland waters. Detailed knowledge is lacking with regard to the composition and structure of various biotic communities in inland waters as well as the physical and chemical nature of those waters as environments for aquatic life.
 Concerning the zoogeography of inland waters in Southeast Asia, the writer has referred to Brehm's work on the freshwater Calanoida as an example. The occurrence of Parabathynella malaya in the subterranean water of Malaya is striking, because this is the only record of this group of Crustacea of the archaic type outside Europe and Japan. Kobayashi's chemical investigations of the river waters of Thailand are a most important contribution to regional limnology in Asia. His work was done at 30 stations which cover all the river systems throughout the country, including two lakes, Lakes Nong Han and Talesaab. The biotic communities of various types of inland waters have been fairly well dealt with by Johnson in Malaya : these are noteworthy for the inhabitants found in peaty black waters, in waters rich in lime, and in torrents at both low and high levels. The effects of human activities upon inland water animal and plant life are also remarkable in many parts of Malaya.
 Production biological studies, which are one of the important research projects in present-day limnology, have been almost neglected in Southeast Asia. In such a situation, Ruttner's plankton studies in the lakes of Indonesia (published in 1953) is especially important. He has shown that the volume of the standing crop of plankton produced at any given moment below a given surface unit of a tropical lake is nearly the same as that of a temperate lake.
 For biologists and limnologists who have had experience of studies only in the temperate zone, tropical inland waters are extremely attractive as they offer great opportunities for the study of many important biological phenomena. It is our hope that Japanese biologists and limnologists will have opportunities to work on inland waters in Southeast Asia using the methods of present-day limnology, and enjoying international co-operation with the biologists and limnologists in those countries.

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