Shredded scrap tires were leached in a modified toxicity characteristic leaching procedure (TCLP) extraction method in synthetic saltwater solutions for three sequential 7-d periods. Test salinities were 5, 15, and 25‰. Acute toxicity tests were conducted with larval sheepshead minnowsCyprinodon variegatusand daggerblade grass shrimpPalaemonetes pugio.Mortality decreased following multiple sequential leaching periods. Toxicity decreased with increasing salinity. The fish were more sensitive than the grass shrimp. Dilution series toxicity bioassays were performed with fish and grass shrimp at 5‰ salinity and at 15‰ with fish only. The 96-h LC50s (lethal concentration for half of the test animals) for fish were 10% leachate at 5‰ and 26% at 15‰. The 96-h LC50 for grass shrimp at 5‰ was 63%. The 96-h lowest observed effect concentrations (LOEC) for fish survival were 12.5% at 5‰ and 25% at 15‰. The 96-h LOEC for grass shrimp survival was 50% at 5‰. Growth LOEC values were 12.5% at both salinities for fish and 50% for grass shrimp at 5‰. Chemical analyses revealed no specific components as the cause of observed toxicity. Antagonism between sea salt and toxic chemicals is hypothesized to cause differential toxicity at varying salinities, as opposed to differential solubility of the toxicants. Extrapolation of laboratory results indicates that proposed tire reefs should not pose a serious threat to water quality in Chesapeake Bay. No observed effects concentrations (NOEC) were an order of magnitude or greater above field concentrations calculated from simplified methods. Toxic substances appear to leach from the surface of the tires not from the tire matrix. The use of tires in higher salinity environments appears to pose little direct toxicological risk to resident organisms. However, because unknown toxic chemicals were present in leachates at all test salinities, no assessment can be made regarding persistence, fate, transport, or possible bioaccumulative effects.