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Acute laboratory toxicity tests were performed on surficial sediments collected from 1176 locations throughout 22 estuarine areas in the United States. Toxicity was determined with three standardized procedures:  10-day amphipod survival tests with solid-phase (bulk) sediments; 5-min microbial bioluminescence tests with organic solvent extracts of the sediments; and either 1-h sea urchin fertilization tests or 48-h mollusc embryo tests with the porewater of the sediments. Test results were weighted to the sizes (km2) of the geographic strata in which samples were collected. Selected bays and estuaries were sampled along the Atlantic and Gulf of Mexico coasts and in southern California along the Pacific coast of the United States. The individual survey areas ranged in size from <1.0 km2 to over 550 km2. Col lectively, approximately 2532 km2 were sampled in the 22 surveys. Toxicity was observed in the amphipod survival tests of bulk sediments in approximately 10.9% of the combined area. These data suggest that acute toxicity as measured with adult crustaceans was restricted to small portions of these urbanized estuaries, principally maritime harbors and industrial ized bayous and waterways. Toxicity was much more pervasive in the tests of solvent extracts and 100% porewater, indicating that approximately 61% and 43%, respectively, of the combined areas sampled were toxic. The spatial extent of toxicity decreased to 11% and 5% in tests of 50% and 25% porewater, respectively. In most areas each test indicated different patterns in toxicity, and consequently, the concordance in estimates of toxicity among different tests was very small. Estimates of the spatial extent of toxicity probably would differ if tests were performed elsewhere and/or with different organisms.