In two villages in a non-urban focus of nocturnally periodic bancroftian filariasis in Thakurgaon thana, Dinajpur District, East Pakistan, Culex pipiens fatigans was found to be the principal vector. Infective mosquitoes were found during 6 months of the year, correlating with other clinical and climatic criteria for a highly endemic focus. These mosquitoes were never found biting cattle. Larvae of this species were found throughout the year in small polluted domestic water collections. Mosquitoes of the Culex vishnui complex were found to be minor vectors of bancroftian filariasis. Infective larvae thought to be Setaria were found in three other mosquito species and infective larvae identical to the bird filarioid, Cardiofilaria nilesi, were present in Culex vagans mosquitoes.
Present address: Office of Medical Services, Department of State, Washington, D. C. 20520.