This research explored the feasibility of ocean disposal of stabilized/solidified (S/S) municipal solid waste (MSW) incinerator ash in organic-rich near-shore marine sediments. A mixture of MSW bottom ash (92%) and fly ash (8%) from a starved-air mass burn MSW incinerator was combined with Type II Portland cement in a 4.54:1 ash:cement ratio. After curing, specimens were cut and placed in centrifuge tubes filled with sediment. Controls containing concrete (cement and sand) specimens and containing sediments alone were also prepared. All samples were incubated in a flow-through seawater system. Over the first ten months of the experiment, the sediment controls reflected conditions similar to those in northern New England estuaries with respect to pH (7.8 ± 0.1), alkalinity (8.7 ± 1.0 meq/L), total dissolved iron (16.7 ± 4.0 mg Fe/L) and SO42-/Cl- (mM) ratios (0.034 ± 0.0025). The S/S ash and concrete control samples exhibited a higher pH (8.9 to 9.6) and more reducing conditions (SO42-/Cl- ratio = 0.015 to 0.020; alkalinity = 3.0 to 5.6 meq/L; total dissolved iron = 0.08 to 0.67 mg/L) in their sediments than the sediment controls. No statistically significant [confidence interval (CI) = 90%] amounts of metals (arsenic, copper, lead, cadmium) were detected in the sediments adjacent to the S/S ash specimens as compared to the controls. Either (1) the metals were not being released from the S/S ash into the surrounding sediment, or (2) they were released but at concentrations below our detection capabilities.