Monitoring of Tampa Bay sediments for organic contaminants has been on-going since 1993 (excluding 1994). This program targets three classes of contaminants: polycyclic aromatic hydrocarbons, which include combustion products of petrochemicals used by automobiles and other vehicles; organochlorine pesticides, which include chemicals such as DDT and chlordane; and polychlorinated biphenyls, which have been used in electrical transformers. Most organochlorine pesticides and polychlorinated biphenyls are no longer produced because of their adverse effects on the environment. Polycyclic aromatic hydrocarbon contamination is almost totally confined to low salinity waters: the Lower Hillsborough River, Palm River, and portions of upper Hillsborough Bay. Some sites in the Hillsborough River have concentrations which are likely to be toxic to aquatic life. The highest concentrations were found in the Hillsborough River near I-275 and near the mouth of the Hillsborough. Polycyclic aromatic hydrocarbons were rarely detected in higher salinity waters and in the coarser, sandier sediments found in most of Tampa Bay. The major source of polycyclic aromatic hydrocarbons to the bay is likely urban stormwater runoff, although incinerators and coal-burning power plants also appear to be sources. The occurrence of pesticides, especially chlordane and DDT, were also generally confined to urban areas (e.g., Lower Hillsborough River, a Culbreath Bayou canal in Old Tampa Bay). Again, low salinity habitats were most affected by pesticides. The majority of Tampa Bay appears unimpacted by pesticides. Sources to the bay appear to primarily be urban stormwater Polychlorinated biphenyls have been found in very high concentrations in the Palm River, in moderate to high concentrations in the Lower Hillsborough River, and low to moderate concentrations in portions of upper Hillsborough Bay. Polychlorinated biphenyls were only rarely detected elsewhere in the bay. In general then, the urban tributaries and residential canals are the areas primarily impacted by organic contaminants; the industrial portions of Hillsborough Bay appear less impacted.