The woolly mouse opossum Marmosa demerarae and the murine opossum, Marmosa murina, occur in sympatry across most of their range; however, they are not syntopic in that M. demerarae is more abundant in the canopy of primary and secondary forest, while M. murina is scansorial and appears to be more abundant in lower forest strata. We herein present a survey and comparison of the helminths occurring in these 2 species in French Guiana based on examinations of 18 individuals of M. murina and 21 individuals of M. demerarae. At the level of the component community, species richness was established at 12 for M. demerarae and 14 for M. murina; the nematodes Pterygodermatites (Paucipectines) elegans and Aspidodera raillieti were established as the most abundant and prevalent species in M. demerarae and M. murina, respectively. Infracommunities in both species had an average species richness of 3.7 and 3.8, respectively. Both species share 12 species of parasites, yet Phaneropsolus philanderi, Pterygodermatites (Paucipectines) elegans, Travassostrongylus paraquintus, Trichuris reesali, and Spirura trinitatis were significantly more frequent in M. demerarae. Infections also included Mathevotaenia bivittata, an unidentified anoplocephalid, and Viannaia venezuelensis, all 3 species of which were more frequent in M. murina.