A brackish water lagoon (ca. 4.5 ha) was treated 6 times, from the last week in June until the first week in August 1982 with a liquid formulation containing Bacillus thuringiensis serotype H-14 toxin. Except during conditions of strong winds, doses of 1.1 to 2.3 kg/ha gave good control of larvae of Anopheles sundaicus, the main vector of malaria in the coastal areas of many islands of Indonesia. Adult populations of An. sundaicus in nearby hamlets were steadily reduced following successful larvicide treatments but readily increased following a control failure.