The NERL Particulate Matter Longitudinal Panel Studies were used to characterize temporal variations of personal exposure to PM and related co-pollutants, including that of PM measured at ambient sites. These studies were fundamental in understanding the associations between personal exposure to PM, PM measured at ambient sites, and health effects, especially for susceptible sub-populations. Projects were designed to evaluate different sub-populations, regions of the country, seasons, and housing conditions. Susceptible sub-populations including chronic obstructive-pulmonary disease (COPD) patients, individuals with cardiovascular disease, the elderly, and asthmatics among others. These studies represented a cooperative effort between the NERL and other scientific organizations. This report documents the progress of field data collections associated with the aforementioned studies and reports preliminary data from those studies where data validation has been completed. Collected data is being used to develop databases representing actual human exposures to particulate matter and related copollutants of ambient origin. These data fill a critical scientific need for the Agency in identifying potentially important exposure variables, as well as providing inputs for modeling and risk assessments.