A study was conducted to address the question of how fish consumption, occupation, and outdoor air affected serum PCB concentrations and congener patterns among 139 Native American men living near three hazardous waste sites. They were interviewed about their residential, occupational, and dietary histories, and donated 20 ml of venous blood for congener-specific PCB analysis. The similarity in the congener pattern between that found in the serum and that detected in local environmental samples was measured by calculating the Euclidean distance between them. The results indicated that serum PCB concentrations were positively associated with cumulative lifetime exposures to PCBs from local fish consumption and occupation. However, participants who lived in the last 10 years at Raquette Point, which is the area of the Reserve closest to the hazardous waste sites and the only location where elevated levels of PCBs were found in outdoor air, did not have higher serum PCB concentrations than participants who lived elsewhere at Akwesasne. Regarding pattern matching, Mohawk men with the greatest cumulative lifetime exposure to PCBs from local fish consumption had a serum PCB congener pattern that more closely resembled that in fish caught off-shore from one of the hazardous waste sites than did men who ate less local fish. Similarly, Mohawk men who were occupationally exposed to PCBs were more likely than those without occupational exposure to have a serum PCB congener pattern that was similar to that of Aroclor 1248, the commercial PCB mixture used locally. The serum PCB congener pattern of Raquette Point residents more closely resembled the pattern in outdoor air only if the men ate relatively few local fish. The study is among the first to demonstrate that outdoor air may affect serum PCB congener patterns, at least in the absence of heavy fish consumption.