1. The results of a survey of 194 Peruvian and Colombian primates for filarial infections are presented. Nine genera and 14 species of marmosets and monkeys are represented in the survey. A blood film survey revealed microfilariae in 82, of 42% of the animals. Adult worms were recovered from 21 of 61 dissected animals. The 209 adult worms belong to four species: Dipetalonema gracile, Dipetalonema caudispina, Tetrapetalonema marmosetae, and Tetrapetalonema tamarinae, a new species.2. New host records for Dipetalonema gracile are: Tamarinus nigricollis, Cebus albifrons, and Saimiri boliviensis. Saimiri boliviensis is a new host for Dipetalonema caudispina. New hosts for Tetrapetalonema marmosetae are: Oedipomidas oedipus, Saimiri sciurea, S. boliviensis, and Ateles paniscus.3. The adult worms and microfilaria of a new species of filarial worm, Teirapetalonema tamarinae, are described from a Peruvian tamarin marmoset, Tamarinus nigricollis.