Microfilariae of Wuchereria bancrofti and Brugia pahangi, which were inoculated into Meriones unguiculatus and Mastomys natalensis respectively, were found in the peripheral blood of the rodents until the ninth day after infection, but no microfilarial periodicity was observed. Microfilariae of W. bancrofti disappeared much faster from the peripheral blood of jirds after reinfection than after the first inoculation. Microfilariae of Dirofilaria immitis inoculated into M. natalensis and laboratory mice were recovered in the peripheral blood until the 17th day after infection and remained infective to mosquitoes. For the first few days the microfilarial periodicity observed in the rodents was similar to that observed in the donor dog, but then reversed.