In the mid 1980s the Australian Centre for International Agricultural Research (ACIAR) committed itself to a program of biological control of the aquatic weed Salvinia molesto in Sri Lanka. Salvinia in Sri Lanka interferes with irrigation and drainage of rice paddies, it reduces the fish catch in water reservoirs and it also poses a health risk in providing additional breeding opportunities for mosquitoes. The agent of biological control is a Brazilian weevil called Cyrtobagous solvinioe. Spectacular results with this beetle have already been achieved in Australia, Papua New Guinea and other countries following entomological work during the 1970s in which the Commonwealth Scientific and Industrial Research Organization (CSIRO) played a pioneering role. This study estimates the economic benefits from the Sri Lankan program.