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Two collaborative studies have been conducted by the U.S. Environmental Protection Agency (EPA) National Exposure Research Laboratory (NERL) and National Health and Environmental Effects Research Laboratory to determine personal exposures and physiological responses to particulate matter (PM) of elderly persons living in a retirement facility in Fresno, CA. Measurements of PM and other criteria air pollutants were made inside selected individual residences within the retirement facility and at a central outdoor site on the premises. In addition, personal PM exposure monitoring was conducted for a subset of the participants, and ambient PM monitoring data were available for comparison from the NERL PM research monitoring platform in central Fresno. Both a winter (February 1-28, 1999) and a spring (April 19-May 16, 1999) study were completed so that seasonal effects could be evaluated. During the spring study, a more robust personal exposure component was added, as well as a more detailed evaluation of physical factors, such as air-exchange rate, that are known to influence the penetration of particles into the indoor environment. In this paper, comparisons are made among measured personal PM exposures and PM mass concentrations measured at the NERL Fresno Platform site, outside on the premises of the retirement facility, and inside selected residential apartments at the facility during the two 28-day study periods. The arithmetic daily mean personal PM[sub2.5] exposure during the winter study period was 13.3 µg/m³, compared with 9.7, 20.5, and 21.7 µg/m³ for daily mean overall apartment, outdoor, and ambient (i.e., platform) concentrations, respectively. The daily mean personal PM[sub2.5] exposure during the spring study period was 11.1 µg/m³, compared with 8.0, 10.1, and 8.6 µg/m³ for the daily mean apartment, outdoor, and ambient concentrations, respectively. [ABSTRACT FROM AUTHOR]