A survey of 2050 seventh- and eighth-grade schoolchildren was conducted in Bochum, Germany, in 1991. The prevalence of wheezing and allergic rhinitis was assessed by self-completed written questionnaires and video questionnaires. To estimate the traffic density on the street of residence, children were asked about the frequency of heavy truck traffic on weekdays and to describe the street either as a main road or as a side street. There was a positive correlation between the prevalence of wheezing as well as allergic rhinitis and the indicators of traffic density, controlling for age, sex, nationality, passive smoking, active smoking, parental history of asthma, and so on. The adjusted prevalence odds ratio (ORs) and 95% confidence intervals (CIs) contrasting the "frequent" and "constant" categories for truck traffic with the "never" category were as follows: for wheezing (written questionnaire), OR = 1.53 (CI: 1.06 to 2.20) and OR = 1.67 (CI: 1.05 to 2.66); for wheezing (video questionnaire), OR = 1.58 (CI: 1.13 to 2.20) and OR = 1.94 (CI: 1.26 to 2.99); and for allergic rhinitis, OR = 1.67 (CI: 1.17 to 2.38) and OR = 1.54 (CI: 0.97 to 2.44). In conclusion, a possible role of factors associated with automobile exhausts causing or exacerbating asthma symptoms and allergic rhinitis in children is supported.