PCBs were determined in water samples from 11 open water sites in Lake Michigan and compared to data from 1980. PCB concentrations declined from 1980 to 1991 with a first-order rate constant calculated to be -0.078 yr(-1). The most southern and southwesterly sites sampled were higher in concentration and exhibited different homolog profiles and partitioning behavior than samples from other sites, The organic carbon-normalized partition coefficients were not correlated to K-ow. A simple mass budget about the water column for 1991 using current measurements of PCB inputs and outputs shows a significant imbalance of PCBs and indicates the need for further study of the roles that subregional atmospheric deposition and sediment-water interactions play as sources to the lake.