Information upon the distribution and biology of the Muridae occurring in Nyasaland (now the Malawi Republic) was obtained mainly from collections made between February 1962 through June 1963, when a total of 13,190 trap nights and 4417 trap days were expended. Approximations of relative abundance in various areas were made by using standard trap lines. Species only recorded in areas with mean annual rainfall at least 60 inches were Lophuromys flavopunctatus, Praomys jacksoni and Thamnomys cometes. Mus triton was unrecorded in areas with mean annual rainfall less than 38 inches. The greatest biomass was trapped on high rainfall plateaux where predominant species trapped were campestrial and insectivorous. In other areas, species predominant in traps were mainly fossorial and vegetarian. In 78% of the localities examined, one or two species comprised over 65% of the catch.
Some details of the bionomics and breeding biology of the common species were elucidated by regular collections in selected areas throughout the annual cycle. Species studied in detail were found to have a reproductive peak during the wet or the first half of the dry season. Males were consistently larger than females excepting in T. cometes, sexual size differences were statistically significant in several species. Of the 32 species recorded, only four were purely vegetarian while six were mainly insectivorous.