A series of 28-day studies investigating PM exposures of an elderly population were conducted in Baltimore, MD, Fresno, CA, and Research Triangle Park, NC. Collection of residential indoor, residential outdoor and ambient monitoring data associated with the subjects living in either communal housing or private homes were performed. Data from the studies were used to compare personal exposures, indoor and outdoor mass concentrations relative to those from central community monitoring sites. Results indicated that with the exception of subjects involved in the Baltimore retirement facility (single apartment building), poor mass concentration relationships between personal to community and indoor to community measures occurred. Data from the RTP study indicated that approximately 45% of the PM2.5 mass measured inside single family homes was the result of ambient origin. Likewise, < 50% of the RTP subjects' total personal PM2.5 exposures could be attributed to ambient sources.