With an improved technique, quantitative inoculation of Brugia malayi microfilariae (mff) into Anopheles sinensis and Culex quinquefasciatus was carried out in our laboratory in 1988. The development of B. malayi mff in these two species of mosquitoes was observed. In the system of B. malayi and An. sinensis, a well-fitted linear correlation appeared between the number of mff inoculated and the infective larva (L3) positive rate (r = 0.9910; P less than 0.01). The regression equation with the regression coefficient of 8.490 suggested a high susceptibility of this species of mosquito to B. malayi even under the condition of experimental inoculation. The quantitative relationship between the number of mff inoculated and the average filarial maturity rate was also exhibited. At the same dosages of 4 and 10 mff/mosquito, the L3 positive rates and the average filarial maturity rates in An. sinensis were much higher than those in Cx. quinquefasciatus (P less than 0.01), indicating significant difference occurred inside the bodies of these two species of mosquitoes.