Seventh-Day Adventists (SDAs), nonsmokers who had resided since 1966 in the vicinity of nine airports throughout California (n = 1,868), completed a standardized respiratory symptoms questionnaire in 1977 and again in 1987. For each participant, cumulative ambient concentrations of fine particulates less than 2.5 microns (microns) in aerodynamic diameter (PM2.5) were estimated from airport visibility data. Long-term ambient concentrations of estimated PM2.5 in excess of 20 micrograms per cubic meter (micrograms/m3) were found to be associated with development of definite symptoms of chronic bronchitis between 1977 and 1987. Estimated mean concentrations of PM2.5 were associated with increasing severity of respiratory symptoms related to general airway obstructive disease, chronic bronchitis, and asthma. It was felt that the observed relationships, with the exception of the relationship between increasing severity of chronic bronchitis symptoms and PM2.5, could be due to surrogate relationships with other ambient pollutants.