Abstract: This paper reports the early development and variation of incculate Brugia malayi microfilariae in 3 groups of mosquitoes,i.e.young Anopheles sinensis,young Culex quin-quefasciatus and old Cx.quinquefasciatus.Significant differences were observed among these groups.Sixty hours after inoculation,the percentage of normally developing filarial larvae in young An.sinensis was 72.3%;the percentage of melanized microfilarise in young Cx.quinquefasciatus was 75.4% and the percentage of filarial larvae which deve-loped abnormally or remained in dispause status in old Cx.quinquefasciatus was 67.1%,each being much higher than that in the other groups.It was suggested that the immune competence of the mosquitces had influence upen the filarial development.The intensity of the immune response not only varied with the species,but also diminished with the aging of mosquitces