One of the primary functions of ecological work is to conduct surveys of those species of vertebrates and/or invertebrates that are involved directly or indirectly in vector-borne diseases of man. The aim in southern Africa has been to contribute to a stable nomenclature at the species level, to determine the range of each species and to make an attempt to single out key environmental limiting factors. Once the taxonomic status and range of the species have been established with some degree of certainty, species may be studied in relation to the distribution and prevalence of any particular disease in order to provide the basis for control. The bio-geographical approach that has been adopted arose when the geographical distribution of human plague derived from wild-rodent sources came to be compared with the distribution of the small mammals and their respective fleas. This threw much light on the factors concerned in the limitation and persistence of plague. These comparative studies were facilitated by plotting the distribution data on grid maps.