In a locality (Sada) of Vasco City, Goa, India, that was highly infested with mosquitoes, weekly spraying of Bacillus sphaericus (strain 101, serotype H 5a 5b) at the rate of 1 g/m2 in polluted water habitats, viz, surface drains, cess pits, cess pools, and septic tanks, resulted in a sharp decline in the immature and adult populations of Culex quinquefasciatus. The per man-hour adult densities, percent habitat positivity, and immature densities were significantly lower (P < 0.001) in the treated area compared to the control area through out the study period.