Measurements of personal exposures to respirable particles (RSP) were obtained from nonsmoking adults living in two rural Tennessee communities. Personal exposure measurements were compared to simultaneously collected indoor (home) and outdoor concentrations. Personal exposures were higher than, had a greater variance than, and were uncorrelated with outdoor concentrations. Household smoking was found to be a substantial contributor to personal RSP exposure. Regressions of indoor concentrations on paired personal exposures explained 11-87% of the variance in exposure depending on employment subgroup and household smoking. A deterministic, predictive model based on the time spent in four microenvironments and measured concentrations explained 64% of the variance in personal exposure. Ambient concentrations provide poor prediction of personal exposure to undifferentiated respirable size particles. Air pollution epidemiological investigations must consider the importance of indoor environments in estimating subject exposures. Further, the chemical/elemental compositions of indoor concentrations and personal exposures are likely to be different from ambient concentrations. This study indicates the potential for misclassification and misassociation of exposures that are likely to result in relying upon ambient, community-based particle measurements.