Cadmium (Cd) toxicity and the effect of Cd exposure on oxygen consumption, accumulation and body biochemical composition of a marine dressinid bivalve Mytilopsis sallei were investigated. The 96 h LC50 of Cd for M. sallei was 0.71 mg/L and the safe concentration was 7.1 microg/L. Exposure of M. sallei to Cd resulted in significant decrease in oxygen consumption with increasing metal concentration. Cd accumulation in M. sallei was sensitive to both concentration and duration of exposure to Cd. In both experiments, the concentration of metal was 3-30-fold higher than the normal level. The effect of exposure time and concentration of Cd on body biochemical composition was also studied in M. sallei. Both carbohydrates and proteins were utilized in concentration as well as time-dependent exposure of Cd to M. sallei. The ratios of glycogen/protein and glycogen/lipid were decreasing with increasing exposure concentration of Cd. In time-dependent experiments, these ratios were observed to be decreasing up to the 4th day, but later (10 and 20 days) there was a recovery with values almost reaching the normal level for glycogen/protein ratio. The caloric concentration levels were determined in M. sallei on exposure to Cd but there was not much change either in time- or concentration-dependent exposure of Cd. The results of the present investigation indicate that these bivalves prefer to depend on carbohydrates and proteins rather than on lipids for their utilization on exposure to either sublethal or lethal stress of Cd. The decrease in oxygen consumption together with the utilization of glycogen and carbohydrates during Cd exposure suggest that these bivalves might shift to anaerobic metabolism in order to encounter the heavy metal stress in the environment.