This project aims at studying the influence of airborne pollution caused by traffic of vehicles and its interaction with adverse indoor environmental conditions, in the development of wheezing diseases, allergy, and atopic sensitization in children having a mother's history of atopy. This is a prospective two-years cohort study of 900 neonates, stratified according to the traffic density of their area of residence and to their families's history of atopy (high traffic areas: 450, with 350 children with a mother's history of atopy and 100 children whose families have no history of atopy; low traffic areas: 450, with 350 children with a mother's history of atopy and 100 children without family history of atopy). 700 neonates (350 from high traffic areas and 350 from low traffic areas, having 100 children in each group with families without history of atopy) will be followed by pediatricians and submitted to diagnostic tests for viral infections in case of wheezing episodes or respiratory infection. All children will be submitted to lung function tests, faeces analysis for protozoa and parasites, and to immune tests to identify the first signs of atopy. The exposure to organochloride compounds will be evaluated in the mother's milk collected in the children's first month of life. The houses of the 700 children will be visited to collect indoor environment samples, to follow the health status of the children, and to collect information on exposure to hazardous agents in the home environment. 200 children with mother's history of atopy (100 from areas with high traffic and 100 from low traffic areas) will not be followed-up by the pediatricians. However, home visits will be performed for monitoring their health status in the first week and at 6, 12, and 24 months of age. This will be a control group. Individual exposures to outdoor air pollution will be estimated by a mathematical model applied to data from the CETESB (air quality parameters), the Traffic Engineering Company (type and volume of traffic), and from meteorological stations located in São Paulo. Thermohygrographs, passive diffusion samplers for NO and NO2, RCS High Flow Air Sampler and a Harvard impactor to collect air samples to quantify fungi and PM10 and PM2,5 will be periodically installed in the houses of the 700 children followed-up by the paediatricians. House dust samples will be collected to quantify allergens and bacterial endotoxins. Building characteristics of the children's houses will be registered, with measurements of natural light, solar orientation and dampness. Information on possible confounding factors will be obtained by questionnaires applied to all 900 children.