Human exposure to Respirable Particulate Matter (RPM, particles less than 5 μm in diameter) was assessed for Low-Income Group (LIG) and Middle-Income Group (MIG) respondents who were monitored for 48-hour integrated exposure in Mumbai, India. Using personal samplers, each respondent was sampled once a week on average from October 2002 to January 2003. An activity diary was recorded and a questionnaire survey carried out by the research team to collect information about workplace and home characteristics. For LIG respondent, the average personal exposure to RPM was 186 μg/m3 (n = 8, Std. Dev. = 184). For MIG respondent, it was 73 μg/m3 (n = 14, Std. Dev. = 39). The Indian National Ambient Air Quality Standard (NAAQS) was exceeded by 86% for LIG respondent. The respirable dust collected on polycarbonate membrane filter was digested and further analyzed for metals using an atomic absorption spectrophotometer. Average lead concentration of 0.284 μg/m3 was much below the NAAQS of 1 μg/m3. Metals concentration data were used for source apportionment using factor analysis technique. The analysis resulted in three factors, represented by groups of metals associated with industrial, residential and crustal sources for all samples combined. A separate factor analysis resulted in two and three sources for MIG and LIG respondents, respectively. The third LIG source represented metals associated with residential living conditions, such as poor ventilation and burning of low-grade fuel. The ambient air concentration for PM10 in the study area was 291 μg/m3 (n = 10). Investigation of source apportionment by statistical analysis can quantify contributions of various indoor and outdoor sources to personal exposure, thus assisting policy makers in developing relevant control and planning strategies.