Prenatal and childhood pesticide exposure has been associated with neurodevelopmental disabilities in a number of studies in low income countries and more recently in the US. Only a few studies have been conducted in children with chronic low-level exposure as may be typical for New Zealand. Given New Zealand's large agricultural industry and extensive mixed agricultural land use pattern, pesticide exposure is likely widespread. We therefore propose to conduct the first study on pesticide exposure and neurodevelopmental effects in New Zealand. We will conduct a questionnaire survey in 300 farmers' children, 300 rural non-farmers' children and 300 urban children. In randomly selected subgroups (150 in each group of children) we will conduct detailed exposure measurements and objective neuropsychological testing. This study will assess the extent of neurodevelopmental health effects related to pesticide exposure in New Zealand children, and will permit the development of preventive interventions.