The toxicity of nitroaromatic (2,4-diaminonitrotoluene [2,4-DANT] and 1,3,5-trinitrobenzene [TNB]) and 14C-labeled cyclonitramine compounds (hexahydro-1,3,5-trinitro-1,3,5-triazine [RDX] and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine [HMX]) to the marine polychaete Neanthes arenaceodentata and the estuarine amphipod Leptocheirus plumulosus following 10- or 28-d exposures to spiked sediments was investigated. Organismal-level effects on survival, growth, and reproduction and cellular-level effects on apoptosis (programmed cell death) were evaluated. Because cyclonitramines have low affinity for sediment, overlying water was not exchanged in the RDX and HMX exposures. Nitroaromatics sorbed strongly to sediment, resulting in near complete resistance to solvent extraction. Cyclonitramines sorbed weakly to sediment, as more 14C-activity was found in the overlying water than in the sediment at exposure termination. No significant decrease in survival or growth was observed with cyclonitramines at initial sediment concentrations as high as 1,000 microg/g. Survival was significantly affected by nitroaromatics at nominal sediment concentrations as low as 200 microg/g, with L. plumulosus being more sensitive than N. arenaceodentata. Growth was significantly decreased at sublethal concentrations of 2,4-DANT for N. arenaceodentata. Reproduction, measured only with L. plumulosus, was significantly decreased only in the highest RDX treatment and also in the lower TNB treatment. However, no decrease was observed in higher concentrations of TNB. Body burden at exposure termination was below detection limit (1 microg/kg) for all compounds. Significant inhibition of apoptosis was not accompanied by significant decreases in growth or reproduction. Because of its critical function in many biological processes. alterations in this endpoint may result in adverse effects on the organism and could be used as an early indicator of toxicity.