Using the indoor simulating method of pollution exposure at various concentrations, the toxic effects of various concentrations of petroleum hydrocarbons (PHCs), copper (Cu2+) and cadmium (Cd2+) on the polychaete Perinereis aibuhitensis Grube and on its acetycholinesterase (AChE) activity were examined. The results indicated that petroleum hydrocarbons, Cu2+ and Cd2+ had the high toxicity to the polychaete Perinereis aibuhitensis Grube. After 4-day and 10-day exposure to petroleum hydrocarbons, Cu2+ and Cd2+, the value of LC50 were 440 and 110 microg x L(-1) for PHCs, 1 150 and 570 microg x L(-1) for Cu2+, 5 090 and 2 500 microg x L(-1) for Cd2+. In particular, PHCs had a stronger acute toxic effect than Cu and Cd. The AChE activity was inhibited, when the animal was exposed to Cd2+ and Cu2+, but the rate of inhibition was less than 50%. In particular, the AChE activity of the animal exposed to PHCs was significantly inhibited. The maximum rate of the inhibition by PHCs reached more than 90%. Moreover, the changes in the AChE activity significantly related with the concentration of PHCs. Thus, the index in the activity of AChE can sensitively reflect the toxic effects of PHCs on Perinereis aibuhitensis Grube as an important biomarker.