Polychlorinated biphenyl (PCB) concentrations in precipitation (1997-2003) and in the atmospheric gas phase (1996-2003) collected in Chicago, IL, are reported. These data were obtained as part of the Integrated Atmospheric Deposition Network. For comparison, PCB concentrations at a remote site, Sleeping Bear Dunes on the northeastern shore of Lake Michigan, are also reported. Much higher PCB concentrations in both precipitation (7.1 +/- 0.9 ng/L) and the gas phase (1.4 +/- 0.1 ng/m3) at Chicago compared to Sleeping Bear Dunes (1.1 +/- 0.1 ng/L and 0.1 +/- 0.08 ng/m3, respectively) indicate that Chicago is a source of PCBs to the Great Lakes. A long-term decreasing trend of PCB concentrations in precipitation was observed at Chicago with a half-life of 6.8 +/- 3.1 years. The corresponding half-life for PCB concentrations in the gas phase was 7.7 +/- 1.1 years. The significant long-term decrease of PCB concentrations in precipitation and the gas phase in Chicago suggests that regulatory efforts are working, at least in this city.