Methods are described for the cryopreservation of third-stage larvae of Brugia malayi. Optimum conditions utilized larvae free from the mosquito host frozen at the rate of -1° or -0.8°C per min in medium containing 9% dimethyl sulfoxide and 0.004 M polyvinylpyrrolidone. Nonfrozen or thawed larvae were inoculated intraperitoneally into jirds (Meriones unguiculatus), the thawed larvae after cryogenic storage for 5–378 days. In general, the percentage of adult worms recovered at necropsy were comparable between the two groups and ranged from a mean of 6–9% of the larval inoculum. In addition, three of four patas monkeys (Erythrocebus patas) inoculated with thawed B. malayi larvae developed patent infections. The cryopreservation of third-stage larvae of Dipetalonema viteae also is discussed.