A technique was devised for removing the adult female Anopheles albimanus, which were potential vectors of malaria, from populations reared for release of sterile males in a coastal area of El Salvador. The adults, chemosterilized as pupae, were held in cages for 48-72 hr after emergence and then offered a blood meal of warm (42-440C) citrated bovine blood containing 0.05% malathion(0,0-dimethyl phosphorodithioate of diethyl mercaptosuccinate; AI3-17034) from natural membrane condoms for 20 min. Comparisons showed that it was possible to remove more than 95% of the females before the field releases; the remaining females would not survive more than a few days, and therefore could not be implicated in disease transmission. With this level of female removal, there was a corresponding loss of approximately 25% of the males available for release.