The islands of Batan and Rapu Rapu in southeastern Luzon, Philippines, were surveyed for filariasis from November 1984 to May 1985. Microfilariae of Bancroftian filariasis were detected in 10.5% of the people over one year of age. Microfilarial rates and intensity of infection were the same for males and females. The highest rates for both sexes were in the 56- to 60-year-old age group. Aedes poicilius, which breeds in abaca and banana plants, was found to be very anthropophilic, comprising 96.5% of the mosquitoes biting man. Ths mosquito bites most frequently in the middle of the night. Dissections showed that 1.0% of Ae. poicilius were infective with third-stage larvae, and each infective mosquito contained a mean average of 5.6. larvae. Keywords: Bacroftian filariasis; Rapu Rapu Island; Philippines; W. bancrofti; Reprints.