between january 2007 and december 2010, the abundance of medium-sized mammals was studied, with special focus on the molina's hog-nosed skunk, conepatus chinga (molina, 1782), at four locations in southern brazil. in this study, transect line methodology was used to obtain data for distance analyses. transects were traveled by car at night, searching with spotlights along the edges of secondary roads in agricultural landscapes. along 1,811 km, we obtained 620 observations of 20 mammal species. the most common species was the exotic european hare, lepus europaeus (pallas, 1778); the highest abundance estimated for south america was observed in one of the study areas, where its density was estimated as 32 individuals/km2. carnivores were the most commonly recorded mammals, represented by 10 species and comprising 51% of all observations. molina's hog-nosed skunk occurred in all study areas, but occurred in sufficient numbers to obtain density estimates in only two of the areas. we estimated 1.4 to 3.8 individuals/km2, in the first density estimate made by the transect method for a member of conepatus in the neotropics. these values are similar to those estimated for north american species of mephitidae. in brazil, c. chinga is apparently more abundant in the pampa biome than in the grasslands of the atlantic forest. for two other carnivores, lycalopex gymnocercus (fisher, 1814) and cerdocyon thous (linnaeus, 1766), we estimated preliminary densities that were similar to those previously cited for different regions.