Lake Burullus is a stressed wetland on the Egyptian Mediterranean coast, impacted by industrial, domestic and agricultural wastes. The polychaete Hediste diversicolor was used as a biomarker of some heavy metals in the lake, particularly Cd, Cu, Pb, and Zn. The levels of these metals were measured in the worms and surrounding sediment. The results indicated wide variation in the contents of heavy metals in the sediment and worms, with higher levels in the worms. The experimental work showed that Hediste diversicolor displayed a pronounced capacity to accumulate Cu and Pb, while the release of metals by the worms occurred at a lower rate. Lead and Copper showed similar mortality to the test-worms (51.7% and 51.6%, respectively) after 7 days at 500 ppm for each metal.