In April 1992 the Darwin City Council approached the Medical Entomology Branch, Department of Health & Community Services to conduct a trial to determine the efficacy of Enviroblox insecticidal blocks against blowflies and their larvae in wheelie bins. These blocks consisted largely of napthalene with 2% permethrin. Initial trials indicated that the insecticidal activity of the blocks was not adequate for effective control (especially of larvae) . A second batch of Enviroblox insecticidal blocks containing 10% dichlorvos with napthalene were tested against blowflies and their larvae. Under the trial conditions these blocks killed blowflies within half an hour and larvae within six hours. Shelltox Ministrips which contain 18.6% dichlorvos were found to kill blowflies and larvae as effectively as the insecticidal blocks. Larvae feeding on organic matter within plastic bags may be protected from the insecticide vapour in the bin air space. However once larvae escape from the bags to search for pupation sites or more food they are likely to come into contact with a lethal dose of insecticide. The report concludes that a trial of the blocks in household wheelie-bins in part of Darwin should be undertaken to confirm the trial results reported here.