We assessed the prevalence of asthma and allergic disorders in 9-11 year old children in Leipzig and Halle in East Germany, and Munich, West Germany. Both East German cities were heavily polluted due to private coal burning and industrial emissions, whereas Munich has moderate industry but heavy car traffic. All fourth grade pupils in Munich (n = 7445) were compared with those in Leipzig, 1990 (n = 1429) and Leipzig and Halle, 1991 (n = 3105). The prevalence of hay fever and skin test reactivity to common aeroallergens was considerably higher in West Germany as compared to East Germany. Furthermore, the prevalence of asthma was also higher in the West German study area. However, when atopy was taken into account, there was no longer a significant difference in the prevalence of asthma between the two parts of the country.