Comparative pathological effects in three species of fish and six species of invertebrates were investigated using a chemically contaminated sediment from Black Rock Harbor (BRH), Connecticut, USA. Substances contained in BRH sediment are known to be genotoxic, carcinogenic, co-carcinogenic and tumor-promoting. Proliferative lesions were observed in winter flounder (Pseudopleuronectes americanus) external, oral and esophageal epithelial surfaces, renal vascular and nephroblastic elements, and the pancreatic islets. Islet lesions included cystic adenomas and a diffuse islet proliferative condition, nesidioblastosis. In addition, pathology was enhanced when winter flounder were fed mussels (Mytilus edulis) previously exposed to BRH sediment. Neoplastic lesions developed in kidney tubule epithelia, gills, some regions of the gastrointestinal tract, neural elements and heart of oysters (Crassostrea virginica) exposed to BRH sediment for 30 days in the laboratory. In addition, renal carcinomas in three oysters had metastasized to the visceral ganglion. (Copyright (c) 1988 Elsevier Applied Science Publishers, Ltd.)