This research project is focused within the Avon Longitudinal Study of Parents and Children (ALSPAC) which was specifically designed to identify features in the environment which influence health and development and ways that the effect of such features may be modified by the genotype of the individual. The proposal is to address a number of questions concerning the aetiology of autism and the autistic spectrum disorders by concentrating on the different traits that are an integral part of these disorders. This will involve determination of associations with immunisations (and mercury exposures), obstetric factors, maternal and infant infections, fetal exposure to toxins and dietary features as well as a study of co-morbidity such as digestive symptoms and the presence of coeliac disease. This baseline study will then be available for specific add on projects which may concern analysis of DNA for specific candidate genes, serum for signs of infection or autoimmune disorderes, or umbilical cord for toxins.