In Saginaw Bay, Lake Huron, about 3.7 metric tons of PCB remain in the active sediment and inputs from the Saginaw River and atmospheric deposition contribute about 1.4 kg PCB per day. In 1977 the U.S. E.P.A. initiated a research effort on Saginaw Bay which was chosen because of the existing PCB contamination, its importance as a commercial and sports fishery, and because, within a relatively small area, many of the limnological processes occurring in the Great Lakes are represented. Therefore, findings from this work might be extrapolated to other parts of the Great Lakes or other similar water systems. This paper presents an analysis of conditions in the bay during 1979 and a projection of future conditions using a dynamic mass balance model. The primary research questions addressed are: (1) whether simulation models of 'total PCB' are sufficiently accurate or whether refined models considering at least mixtures are necessary, (2) whether volatilization of PCB is occurring, and (3) what is the expected longevity of PCB in the system.