Concentrations of seven heavy metals were determined in green mussels (Perna viridis) collected between April and June 1995 from eight locations along the costal area of the Gulf of Thailand. The average concentrations (n = 96) of the heavy metals detected in mussel samples, on the basis of dry weight, were 1.20 mg kg-1 cadmium, 0.78 mg kg-1 for chromium, 9.85 mg kg-1 for copper, 1.09 mg kg-1 for lead 2.78 mg kg-1 for manganese, 1.54 mg kg-1 for nickel, and 94,48 mg kg-1 for zinc. The levels of cadmium, chromium, nickel, and lead found in green mussels from four locations in the Upper Gulf were significantly (P < 0.05) higher than those detected in mussels from four locations in the Lower Gulf, while the levels of copper, manganese, and zinc did not differ significantly (P > 0.05) between the Upper and Lower Gulf. Comparison with earlier studies revealed that the concentrations of some metals in the mussels collected from the Upper Gulf are increasing. The concentrations of heavy metals in green mussels from the Gulf of Thailand were within acceptable levels for human consumption.