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Background: Mt. Oyama on Miyakejima Island erupted in June 2000 and all Miyake village citizens were forced to evacuate the island in the September, due to continuous eruptions and emission of unsafe amounts of volcanic gas, mainly sulfur dioxide (SO2). Beginning in February 2005, residents returned to live on the island despite the fact that volcanic gas was still being emitted., Objective: To examine changes in the respiratory systems of included children from February 2006 to November 2006., Methods: The study population was 141 children who participated in health checkups in November 2006, including 33 SO2 hypersusceptible children who had a current or past history of asthma, obstructive lung function, current symptoms of whistling and wheezing, and/or deterioration of respiratory symptoms. Respiratory effects were evaluated by a questionnaire for respiratory symptoms and by spirometry. SO2 was monitored at 7 sampling points within inhabited areas, and the mean SO2 concentration from February 2005 to November 2006 was 0.031 ppm. The area was categorized into four areas by average SO2 concentration, namely, areas L, H-1, H-2, and H-3, where the average SO2 levels were 0.019, 0.026, 0.032, and 0.045 ppm, respectively., Results: Compared to children in area L, the frequencies of "phlegm" and "irritation of the nose" were significantly greater in the children in areas H-2 and H-3. %FVC and %FEV1 in hypersusceptible children were significantly reduced in November 2006 as compared to February 2006 (P = 0.047, 0.027), though no reduction observed in normosusceptible children., Conclusion: Respiratory functions in hypersusceptible Miyakejima children may be affected by SO2 exposure, and further follow-up observation is necessary.