As part of an ongoing longitudinal study of air pollution and respiratory function in children, Dr. Gilliland and colleagues, of the Respiratory Core, investigated the effects of passive smoking exposure on the risk of asthma. Information on smoke exposure was obtained from questionnaires asking simple yes/no questions about smoking status of each parent, at various times in the child's life. It was found that asthma risk was associated with in-utero exposure to maternal smoking (relative risk of about 2) but is not associated with smoking exposure post-birth. That smoking may have an effect on fetal development has support from a number of studies. In particular, it is known that detoxification of smoking contaminants is mediated by GST-T1 and GST-M1 genes. In order to validate the in-utero exposure finding and to assess the potential effect modification by the GST genes is currently being undertaken. Dr. Langholz has designed a counter-matched study of prevalent early childhood asthma cases. Detailed parental smoking histories are being obtained as well as buccal cells in order to determine GST-T1 and GST-M1 allelic type.