An epidemiological survey was made in the city of São Lourenço da Mata, in Pernambuco, in december 1963, in order to evaluate the prevalence of bancroftiasis. The survey consisted of: a) blood examination of a representative sample of the human population; b) indoor captures of mosquitoes and c) dissection of these insects. Of 2 459 examined person (23.38%) of the population, 17 (0.7%) exhibited embryos of Wuchereria bancrofti, the only species of filaria found. The blood sample, 20 cubic millimeters, were taken at night, between 7 to 11 p.m. Of 356 houses scarched for mosquitoes, where blood samples were taken, 79.77%, were positive for Culex pipiens fatigans. The captures were made from 6 to 8 a.m. Among 754 fatigans examined for filariae larvae, 1.06% harbored evolutive forms of W. bancrofti.