Swamp wallabies have dramatically extended their distribution through western Victoria and south-eastern South Australia over the last 40 years. Newspaper reports from 1875 onwards show that on European settlement, wallaby populations were confined to eastern Victoria, including the ranges around Melbourne, the Otway Ranges and Portland District of south-western Victoria, and a tiny part of south-eastern South Australia. Populations contracted further with intense hunting for the fur trade until the 1930s. In the late 1970s, however, wallabies began spreading into drier habitats than those initially recorded. Possible causes underlying this change in distribution are discussed; some seem unlikely but, because wallabies began spreading soon after the introduction of European rabbit fleas as vectors of myxomatosis, the cumulative effects of releases of biological agents to control rabbits appear important. A caution is given on assuming that thick vegetation in high-rainfall areas provides the only habitat suitable for swamp wallabies, but, most importantly, the study shows how native mammals may benefit if rabbit abundance is reduced.