Re-suspension of particulate matter (PM) from indoor activities could be a more important source of human exposure to PM than has been previously credited. This seminar discusses a set of experiments and analyses designed to estimate the source contribution of indoor activities to human exposure. We collected indoor, outdoor and personal PM measurements for 5 consecutive days in April 2000 using both real-time laser particle counters and integrated filter samples in a California home. During the first three days, we performed a series of scripted activities. The last two days represent more typical activity levels in the home. We developed source strengths for each of the scripted activities from the particle counter data in accordance with the method outlined by Brauer et al. (JEAEE, 2000). We also used the particle counter time series as inputs for an indoor-outdoor model derived from the mass balance equation to estimate the outdoor contribution to the indoor concentration. The filter samples were analyzed for elemental ions using inductively coupled plasma with mass spectrometry (ICP-MS). We input the resulting elemental source profiles into the Desert Research Institute's Chemical Mass Balance Receptor Model Version 8 (CMB8) to estimate the relative contributions of outdoor air and indoor activities to human exposure. In the absence of other indoor sources, both the indoor-outdoor modeling and the CMB modeling results showed that during human activity periods nearly all the human exposure to PM5 is from the human activities. On days with more typical activity levels, between 60 and 70 percent of the indoor PM5 was due to human activities. The results of this preliminary study support further investigation to characterize human activities and their effect on human exposure to PM.