In children aged 7-9 years residing in the town of Chorzow (C) and in the town of Mikolow (M), located 30 km apart (Upper Silesia, the industrial part of Poland), respiratory symptoms were ascertained according to the parental answers to WHO-Questionnaire. Mean annual concentrations of air pollutants are higher in Chorzow than in Mikolow, and recent mean values of 24 hr measurements over November 1992-January 1993 confirmed the between-town gradient (p < 0.001) for particulates (C:166 micrograms/m3); M:129 micrograms/m3), SO2 (C:153 micrograms/m3); M:92 micrograms/m3) and NO2 (C:69 micrograms/m3); M:26 micrograms/m3). In Chorzow 24.8% (n = 1,142) and in Mikolow 25.6% (n = 480) of all eligible children aged 7-9 years were examined. Both groups (C and M) were similar in terms of sex, family history of asthma and cough lasting for 3 months (C:31.6%; M:32.3%). Frequency of the following respiratory symptoms statistically significantly (p < 0.05) differed between two groups: chest wheezing (C:21.4%; M:17.1%) and attacks of asthmatic dyspnea (C:10.3%; M:6.2%). Also, the diagnosis of asthma by physician was more prevalent in Chorzow (C:3.5%; M:1.3%; p < 0.05). Logistic regression analysis showed that after controlling for family history of asthma, environmental tobacco smoke and housing condition, the place of residence (C versus M) was statistically significantly associated with attacks of asthmatic dyspnea (p < 0.05) and a "borderline' significance of this factor was found in relation to wheezing (p = 0.06) and physician-diagnosed asthma (p = 0.07). The survey provided the estimate of the prevalence of chronic respiratory symptoms in children living in the most polluted urban area of Poland. Although the design of the study precludes more specific etiologic conclusions on environmental exposures the apparently higher prevalence of symptoms in children living in a more polluted town deserves further investigation.