Three species of estuarine invertebrates, Palaemonetes pugio (grass shrimp), Pagurus longicarpus (hermit crab) and Argopecten irradians (bay scallop), were exposed to Cd in flowing seawater at concentrations of 0.06, 0.12, 0.25, 0.5 and 1.0 mg/litre. Incipient LC50 values of 0.53 and 0.07 mg/litre were estimated for bay scallop and hermit crab, respectively. The toxicity curve for grass shrimp had not stabilized, but the incipient LC50 value was estimated to fall within a range of 0.2 to 0.3 mg/litre. Short-term response, as measured by time to 50% mortality at the highest Cd concentration, was 10, 21 and 23 days for the bay scallop, hermit crab and grass shrimp, respectively. Scallop growth was inhibited at all exposure concentrations with a measured 42-day EC50 value of 0.078 mg/litre Cd. Byssal thread detachment precedes death in bay scallops. An EC50 value of 0.54mg/litre Cd for gyssal detachment was measured on day 8 of the bioassay before appreciable mortality. This compared favorably with the incipient LC50 value of 0.53mg/litre Cd. Cadmium accumulation occurred at all concentrations in bay scallop and grass shrimp.