The blow fly community was surveyed in the coastline of Río de la Plata at an ecological reserve in Buenos Aires city. Samples were taken monthly (September 2003 to August 2004). Dog faeces and rotten cow liver were used as baits and their attractiveness compared regarding overall number, species and sex preferences. Cochliomyia macellaria, Phaenicia cluvia, and Sarconesia chlorogaster were dominant. The remaining species recorded were scarcely represented (< 20 %). Number of specimens taken from faeces and liver did not show significant differences. Numerical trends were similar between both baits. Regarding species' preference, C. macellaria was more abundant on faeces while S. chlorogaster preferred liver, while Phenicia cluvia did not show a definite trend. In total, females were more abundant than males. C. macellaria and P. cluvia's sex ratio was female biased; S. chlorogaster did not exhibit sexual asymmetries. A comment was given on the potential sanitary impact of the dominant species.