Death certificates issued in Yokkaichi, during the 36 years from 1963 until 1998 were surveyed to determine the relationship between changes in air pollution and mortality due to chronic obstructive pulmonary diseases. The following results were obtained : 1) In response to worsening air pollution, mortality for bronchial asthma and chronic bronchitis began to increase. 2) Mortality due to bronchial asthma decreased immediately in response to improvement of pollution, whereas mortality due to chronic bronchitis decreased to the level in the control area 4 to 5 years after the concentration of sulfur dioxide (SO_2) began to satisfy the ambient air quality standard. 3) In the polluted area, mortality due to bronchial asthma in subjects who were 20 years of age was higher during the period in which higher concentrations of sulfur oxides were prevalent.
