AbstractSamples of marine subtidal sediments collected in 1985 and 1986 from Elliott Bay, Washington, were analyzed at the Environmental Laboratories of the Municipality of Metropolitan Seattle as part of a larger study. Interstitial water and solvent extracts of subtidal sediments were analyzed by the Microtox procedure to determine toxicity. Particle size distribution, and concentration of oil and grease, metals, and polynuclear aromatic hydrocarbons, were compared to toxicity of interstitial water and solvent extracts. Physical and chemical compositions of sediments affects the toxicities of solvent extracts and interstitial water extracts differently. Samples with smaller particle sizes had relatively high concentrations of oil and grease and metals, and less toxic interstitial water. Samples with larger particles had less oil and grease and metals, and more toxic interstitial water. The opposite was true for the solvent extracts: samples with smaller particle sizes with relatively higher concentrations of oil and grease and metals had more toxic solvent extracts. Samples containing larger particles with relatively lower concentrations of oil and grease and metals had less toxic solvent extracts. No correlations were found between the toxicity of the solvent extracts and polynuclear aromatic hydrocarbons. The Microtox procedure has the potential to estimate toxicity of both water‐soluble and solvent‐soluble compounds in marine sediments if two different extraction procedures are u