Background.Previous research on air pollution effects has found associations with chronic adverse health effects even at the relatively low levels of ambient particulates currently measured in most urban areas.Methods.We assessed the impact of declines of total suspended particulates and sulfur dioxide in eastern Germany after reunification on the prevalence of nonallergic respiratory disorders in children. In the 1990s, particle mass (total suspended particulates) and sulfur dioxide declined, whereas number concentrations of nucleation-mode particles (10–30 nm) increased. In three study areas, questionnaires for 7,632 children between 5 and 14 years of age were collected in three phases: 1992–1993, 1995–1996, and 1998–1999.Results.Adjusted odds ratios (ORs) and 95% confidence intervals (CIs) for a 50-&mgr;g/m3increment in total suspended particulates were 3.0 (CI = 1.7–5.3) for bronchitis, 2.6 (CI = 1.0–6.6) for sinusitis, and 1.9 (CI = 1.2–3.1) for frequent colds. The effect sizes for a 100-&mgr;g/m3increment in sulfur dioxide were similar. The effect estimates for ambient total suspended particulates and sulfur dioxide were stronger among children not exposed to gas stove emissions, visible molds or dampness, cats, or environmental tobacco smoke.Conclusions.The decreasing prevalence of nonallergic respiratory symptoms, along with improvements in ambient particle mass and sulfur dioxide (but not in nucleation-mode particles), indicates the reversibility of adverse health effects in children. This adds further evidence of a causal association between combustion-related air pollutants and childhood respiratory symptoms.