Evaluates the risks to human health and the environment posed by exposure to isobenzan. This cyclodiene insecticide was manufactured in the Netherlands from 1958 to 1965 and used from existing stocks for several years thereafter. Present sources of human and environmental exposure are restricted to the original waste-disposal sites and to polders which were built up using mud dredged from contaminated harbour areas. Although recent research on this insecticide has been limited, the report draws heavily on a number of proprietary toxicological studies made available by the manufacturer.