Abstract: Methods are studied for the cryopreservation of microfilariae (mf) and third-stage larvae (L3) of periodic Brugia malayi. RPMI-1640 tissue culture medium containing 6% dimcthyl sulfoxide (DMSO) and 15% newborn calf serum were used as cryoprotectant.The larvae survived best when specimens were frozen at the rate of -0.5℃ to -1.0℃ per minute using the vapor phase of liquid nitrogen, when the temperature rea-ched - 70℃ to - 90℃ the specimens were placed directly into the liquid nitrogen (-196℃).After the thawing of the mf which had been stored for 6212 and 375 days in cryogen, 26.2% of the mf were shown to be viable and developed in Aedes togoi. It was also shown that the survival rate of L3 cryopreserved for 28-321 days was also S6.2% and that, wben 107 L3 frozen for 321 days were inoculated after being thawed into one jird, one live female adult was recovered at awopsy 71 days after inoculation, its morphology being the same as the unfrozen specimens.There was no correlation between the time of cryopreservation and the survival rate of the larvae.