The possible relationships between ambient pollution and respiratory outcomes among school children in the metropolitan area of Durban, South Africa, were studied. Those residing in the "South" (South Durban) were compared to those in the "North". There was a stronger association between increased NO and NO2 and decrements in peak expiratory flow and forced expiratory volume at one second among children with persistent asthma, as compared to those without persistent asthma, although this relationship was not statistically significant among this smaller group of children. The differences in lung function between the north and south do not appear likely to be explained by differences in persistent asthma rates, since including persistent asthma as an effect modifier did not show a difference. Adjusting the models for persistent asthma suggested that the effects of NO and NO2 exposure on those with or without persistent asthma are not much different. This is an abstract of a paper presented at the 102nd Air & Waste Management Association Annual Conference and Exhibition (Detroit, MI 6/16-19/2009).