The anuran fauna of Borneo consists of 156 known species distributed in almost every potential microhabitat in the forested environments that formerly covered the island. Seven of these species are commonly encountered along almost every stream in forests below 750 m above sea level. Aspects of the natural history of these seven--Bufo asper, Limnonectes ibanorum, L. ingeri, L. kuhlii, L. leporinus, Rana megalonesa, and R. signata--are presented based on observations made at 25 localities scattered through Brunei and the Malaysian states of Sabah and Sarawak. Each species shows wide variation in activity (as measured by numbers seen) within and between streams within localities. Recapture of marked individuals of B. asper, L. ibanorum, L. ingeri, and L. leporinus permits estimation of growth rates and time to sexual maturity and, less certainly, to a coarse estimate of the length of reproductive life. Each of these four species showed extremely wide variation among individuals in terms of movements between successive capture points, with some individuals moving very long distances (within a single stream) and others scarcely moving at all. Although all seven species occur within primary and secondary hill forests, two are apparently restricted to such habitats, while the others also occur in flat, alluvial forests. Four have also been found in plantations of Acacia mangium and three in swamp forests.