Adenylate energy charge is an indication of the amount of energy available to an organism from the adenylate pool. It is calculated from measured concentrations of three adenine nucleotides, adenosine triphosphate (ATP), adenosine diphosphate (ADP) and adenosine monophosphate (AMP), which are integral to the energy metabolism of all organisms (Atkinson 1977). The AEC, defined as (ATP + 1/2 ADP)/ (ATP + ADP + AMP), has a maximum value of 1.0 when all adenylate is in the form of ATP and a minimum value of 0 when all adenylate is in the form of AMP (Atkinson and Walton 1967). Therefore, a knowledge of the energy charge of key species with known responses to particular environmental conditions may provide a convenient measure to assess the extent to which these species are stressed. Sediment from a relatively clean site in Long Island Sound and a highly contaminated sediment from Black Rock Harbor, Connecticut which contained high concentrations of PCBs, PAHs and some metals were used to determine if any observable stressful effect, as indicated by AEC, was due to the physical action of the suspended material rather than to a toxic compound.