Analysis of the helminthofauna of two Didelphis marsupialis, compared to that of a Metachirops opossum from the same area, studied by Durette-Desset, 1974. Except for their similarities in the general repartition of the species, the two Marsupials are easily differentiated: the dominant species is not the same. The location of common or "vicariant" species is stable. In opposition to former notions, the fauna appears to be composed of but one lineage, except for Moennigia, which would appear as captures from Xenarthes.