Abstract: The transmission role of the residual microfilaremia cases was studied in Pingle Village, Liangqing Township, Yongning County where bancroftian filariasis had been virtually eradicated during 1984-1988. The results indicated that after the microfilarial rate of the human population met the criterion of elimination of f ilariasis, namely below 1% of the total population in all the administrative villages, and the average density of microfilana being around 5 per 60μl peripheral blood, subsequent control measures might be no Ion- ger instituted while the microfilaria rate and its density could continue to decline. Some residual microfilaremiae cases having higher microfilarial density turned negative gradually, so did the natural infection rate of Culex quinquefasciatus with filaria larvae and its density year by year. No filaria larvae were found in vector mosquitoes in 1987-1988. The authors deemed that the filariasis transmission in this area has been interrupted.