This paper reports concentrations of DDT residues and dieldrin in surficial sediment, unfiltered near-surface water, intertidal mussels, and epibenthic and pelagic organisms collected from Richmond Harbor more than 25 years after removal of the predominant local source of these contaminants. High concentrations were measured in most of the samples collected. Despite the large concentration gradients away from the source zone, relatively little variability in the tissue/water bioconcentration factors for the mussel, a benthic Gobiid fish, and the pelagic shiner surfperch was observed. This indicates that these organisms are potentially useful bioindicators of organochlorine contamination in estuarine ecosystems.