A series of experiments were instituted in order to clarify the life history of Oswaldocruzia sp., a nematode of frogs. Suitable hosts were collected and examined for the nematode. Artificial infection of laboratory reared frog tadpoles and young frogs by use of incubated juvenile stages of the parasite was undertaken with negative results. Several reasons are suggested to explain failure of infection attempts. The likelihood that juvenile Oswaldocruzia used experimentally were not infective stages of the parasite is suggested. Morphological characters of the worms support this idea. The possibility that tadpoles and young frogs are refractory to infection, and involvement of an intermediate is discussed. Morphology of adult and juvenile Oswaldocruzia is outlined, and comparisons to recorded descriptions are made.