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In this paper, we present results from the SAPALDIA study (Swiss Study on Air Pollution and Lung Diseases in Adults) regarding associations between lung function [forced vital capacity (FVC) and forced expiratory volume in 1 second (FEV1)], as assessed during the cross-sectional study in 1991, and average levels of NO2exposure within the eight study communities. We distinguished average home outdoor exposure and average personal exposure to NO2and obtained exposure estimates by computing regional averages of passive sampler measurements performed by a random subsample of SAPALDIA participants in 1993. Previous analyses had revealed associations between average lung function and average air pollution levels between communities. The present results show that such associations may also be seen within communities: a 10-μg per m3increase in average home outdoor and personal exposure to NO2between zones of residence of the same community was associated with a change in average FVC by −0.59 [95 confidence limits (CL) = 0.01, −1.19] and −0.74 (95 CL = −0.07, −1.41), respectively. These values, however, are smaller than the ones found for the corresponding associations between study communities: −1.67 (95 CL = −1.01, −2.33) and −2.93 (95 CL = −2.11, −3.75), respectively. The different magnitudes of these two types of associations might be explained by differences in spatial variation between various components of air pollution. (Epidemiology 1998;9:405–411)