Antarctica is regarded as one of the most pristine parts of the Earth but even this remote ecosystem is affected by contamination and high levels of certain heavy metals, such as cadmium, which may occur naturally in Antarctic waters. The bivalve scallop Adamussium colbecki is considered a key species of Antarctic benthic ecosystems and a sensitive target for bioaccumulation of xenobiotics and metals. Since cholinesterases (ChEs) in the adductor muscle of A. colbecki presumably play a prominent physiological role through regulation of swimming movements, the main aims of this study was to characterize ChE activities in adductor muscle of A. colbecki and to investigate their sensitivity to organophosphate pesticides and heavy metals. The results suggest that an acetylcholinesterase-like enzyme in the adductor muscle of the scallop has low sensitivity to organophosphates but was significantly inhibited by exposure to cadmium.